general help on 250 to 305 swap

[Bjj_junkie]

hello everyone. i have a 72 with a 250/3 speed in it. i just bought a 305/350 combo. id like to get some general info on more or less what ill need for the swap and what you guys recommend. i know ill need motor mounts and stuff but will i need frame stands and motor crossmember? please excuse me but in all honesty i know very little about this stuff. i kinda jumped into this project blindly and I'm learning as i go but i have very little knowledge. i have a few friends that are into map cars and are helping me a bit but they don't know much about this stuff either. I'm kinda on a budget if not id pay someone to do it and I'm actually paying someone to store it since i live in a apt so the sooner i do this the better. just a general run through and more or less what ill need would be very welcome. thanks a lot

[EARNHARDT#3]

Is there something wrong with the 250? I can't see going through all that trouble to put in a 305.

[Bjj_junkie]

Originally Posted by EARNHARDT#3

Is there something wrong with the 250? I can't see going through all that trouble to put in a 305.

the 250 is fine but the transmission isn't. needs to be rebuilt and this combo cost me the same as the rebuild. i figured it would be a better options since i wanted the truck auto from the get go. i know ill need to invest some more in mounts and shifter but ill try to get something out of the 250 once its out

[mechanicalman]

Originally Posted by Bjj_junkie

hello everyone. i have a 72 with a 250/3 speed in it. i just bought a 305/350 combo. id like to get some general info on more or less what ill need for the swap and what you guys recommend. i know ill need motor mounts and stuff but will i need frame stands and motor crossmember? please excuse me but in all honesty i know very little about this stuff. i kinda jumped into this project blindly and I'm learning as i go but i have very little knowledge. i have a few friends that are into map cars and are helping me a bit but they don't know much about this stuff either. I'm kinda on a budget if not id pay someone to do it and I'm actually paying someone to store it since i live in a apt so the sooner i do this the better. just a general run through and more or less what ill need would be very welcome. thanks a lot

I assume this is a 2WD.

Did you buy this combo because you wanted BOTH the auto trans and the V8? There are issues with both in terms of installation, however you could do one or the other without doing both no problem. IMO the engine is easier than the trans, both are complicated.

I believe the engine cradle is the same, however the 6cyl perches, I have read, will locate the engine farther back than the small block V8's were originally. I have read that they do give enough clearance for a small distributor but get either tight or actually hit the firewall if you use the larger HEI; the V8's came from the factory with smaller points distributors; I expect the 305 has an HEI. I have read the V8 perches are different than the inline 6 perches. I have also read conflicting reports so there it is clear as mud.

To complicate the installation, I assume you will be using the accessories on the 305 and that would likely be the longer water pump. That will put the alternator on the passenger side as opposed to the driver's side, as long as the wire reach then no problem. If you have A/C, then the compressor would be on the driver's side as opposed to the factory passenger side, so you would need the appropriate A/C hoses to reach across the engine bay.

If you are going to run a floor shifter for the automatic, that un-complicates things a bit. If you are going to run a factory steering column with automatic shifter, you have to stick to a factory configuration assure the trans is in the right position to line up with the pivot bracket on the frame. I have read there are two different positions for the bracket as long as it's in one of them. You will also need an automatic trans rear cross-member.

You will also need to remove the cross-member that holds the rear engine mounts to the bell housing. I'd recommend while the engine is out to use a big air hammer with a hardened chisel to remove the forged rivets. You can also cut them off with a torch or a die grinder then pound them out with a round flat chisel. Or, use a sazall and cut as close to the frame as you can but to me that looks ghetto.

If you still have points on the 6, you will need to replace the resister wire from the fuse block to the coil with a 12ga wire to the HEI.

And then there is the driveshaft length issue.

I expect there may be some way to start at the driveshaft and work your way forward to avoid having to alter the length of the driveshaft, but I'm not sure. Maybe someone that actually knows will chime in and un-complicate this for you.

If you don't mind a little trial and error, you could get the auto trans cross-member, drop the engine/trans in with the driveshaft you have now first see if you have distributor clearance at the firewall then see if the trans linkage bracket lines up or it it will line up in the alternate position then if all looks well drill the holes in the frame for the trans crossmember if they are not there already. Then holding up the engine with a floor jack (2x8 chunk protecting the oilpan), line up the engine perches and/or replace them as necessary. Then use the appropriate fan shroud to accommodate your fan and extra water pump length, or change the fan to fit the shroud after the depth issue is addressed, factory fan shroud can be shortened if necessary.

And, you will need a new radiator and trans cooler lines. Oh, and hopefully your new steering column or shifter assembly will come with the proper backup light and neutral safety switch.

You will need a new exhaust system to fit the 305 manifolds.

I'm sure there are yet more details, but I cannot recall them all.

[Bjj_junkie]

Originally Posted by mechanicalman

I assume this is a 2WD.

Did you buy this combo because you wanted BOTH the auto trans and the V8? There are issues with both in terms of installation, however you could do one or the other without doing both no problem. IMO the engine is easier than the trans, both are complicated.

I believe the engine cradle is the same, however the 6cyl perches, I have read, will locate the engine farther back than the small block V8's were originally. I have read that they do give enough clearance for a small distributor but get either tight or actually hit the firewall if you use the larger HEI; the V8's came from the factory with smaller points distributors; I expect the 305 has an HEI. I have read the V8 perches are different than the inline 6 perches. I have also read conflicting reports so there it is clear as mud.

To complicate the installation, I assume you will be using the accessories on the 305 and that would likely be the longer water pump. That will put the alternator on the passenger side as opposed to the driver's side, as long as the wire reach then no problem. If you have A/C, then the compressor would be on the driver's side as opposed to the factory passenger side, so you would need the appropriate A/C hoses to reach across the engine bay.

If you are going to run a floor shifter for the automatic, that un-complicates things a bit. If you are going to run a factory steering column with automatic shifter, you have to stick to a factory configuration assure the trans is in the right position to line up with the pivot bracket on the frame. I have read there are two different positions for the bracket as long as it's in one of them. You will also need an automatic trans rear cross-member.

You will also need to remove the cross-member that holds the rear engine mounts to the bell housing. I'd recommend while the engine is out to use a big air hammer with a hardened chisel to remove the forged rivets. You can also cut them off with a torch or a die grinder then pound them out with a round flat chisel. Or, use a sazall and cut as close to the frame as you can but to me that looks ghetto.

If you still have points on the 6, you will need to replace the resister wire from the fuse block to the coil with a 12ga wire to the HEI.

And then there is the driveshaft length issue.

I expect there may be some way to start at the driveshaft and work your way forward to avoid having to alter the length of the driveshaft, but I'm not sure. Maybe someone that actually knows will chime in and un-complicate this for you.

If you don't mind a little trial and error, you could get the auto trans cross-member, drop the engine/trans in with the driveshaft you have now first see if you have distributor clearance at the firewall then see if the trans linkage bracket lines up or it it will line up in the alternate position then if all looks well drill the holes in the frame for the trans crossmember if they are not there already. Then holding up the engine with a floor jack (2x8 chunk protecting the oilpan), line up the engine perches and/or replace them as necessary. Then use the appropriate fan shroud to accommodate your fan and extra water pump length, or change the fan to fit the shroud after the depth issue is addressed, factory fan shroud can be shortened if necessary.

And, you will need a new radiator and trans cooler lines. Oh, and hopefully your new steering column or shifter assembly will come with the proper backup light and neutral safety switch.

You will need a new exhaust system to fit the 305 manifolds.

I'm sure there are yet more details, but I cannot recall them all.

thank you, yea ill be doing a floor shifter and the person i bought the engine from included the exhaust system and radiator.

[SS Tim]

Three speeds are kind of hard to kill. Are you sure it isn't just a linkage issue?

[Bjj_junkie]

Originally Posted by SS Tim

Three speeds are kind of hard to kill. Are you sure it isn't just a linkage issue?

i was told its internal. i don't know myself but thats all i was told

[SS Tim]

In that case I'd try to confirm the trans issue. Then, if needed, stuff in a used three speed to sort and drive the truck.
They can be found cheap if not free for the asking sometimes. Then you can plan out you engine and trans swap with a lot more information on where you want to go and how it get there. Workable vs factory style change over a big difference. Either are more than a weekend project.