swapping to a big block from a 6 cylinder 4 speed
 

Forgive me if this has been posted a million times...

The truck is a 1969 C-10 shortbed. It currently has a 350 installed in what seems to be the original 6 cylinder mounts. I believe this because the engine is very low and far back in the engine compartment. But the clutch and transmission works great, and looks to be in the original location, based on how the bellhousing is bolted to the crossmember... My plan is to install a 402 I have from a parts truck, using new big block mounts and towers, and to keep the 4 speed.

What challenges are there in keeping the riveted in crossmember from the original straight 6 and 4 speed transmission? do you have to cut that crossmember out and would the transmission have to be moved backwards or forwards?

The main concern I have is the transmission crossmember that is riveted in, seems to be necessary to support the bellhousing etc, and seems like it would be tough to install the big block without taking it off. Do the big block towers actually locate the engine in exactly the right location? What have you guys done when keeping the original granny low 4 speed for this conversion?

Any suggestions would be very helpful, thanks!

Re: swapping to a big block from a 6 cylinder 4 speed
 

I can't help with the BB location but I can tell you the crossmember isn't a big issue. Pop the rivets out and bolt it in where you want it if it's not in the right place. Most of the trucks I have had didn't have the original rivets anymore because someone before me had removed them and replaced with bolts.

Re: swapping to a big block from a 6 cylinder 4 speed
 

Note on above: There isn't a transmission crossmember on a truck with a 4 speed - it is a bellhousing crossmember and I don't think it can be moved. The transmission hangs from the bellhousing.
I haven't done a big block install with a 4 speed truck transmission so can't help you with specifics, but I don't see what the difference would be other than mounts. I am sure someone who has done it will chip in.

Re: swapping to a big block from a 6 cylinder 4 speed
 

I would drop it in those 6 cyl mounts. You may have to do a little massaging on the firewall to clear your distributer, and valve covers, but it would be a lot easier than moving the trans crosmember, and redoing the clutch linkage, driveshaft etc...