'68 6 cyl to 468 swap with 4 speed sm465

[jhyder408]

so I need an expert answer to this question, removed 250 6 cyl and motor mounts, installed a 468 to the existing sm465 4spd, my motor mounts are back as far as possible but there is still a gap between my bell housing and engine. I noticed a second set of holes that move the 4 speed cross member forward about 3 inches or so. Is one set for 6cyl and the other for v8's?? do I need to move the trans to those fwd holes?

[jhyder408]

bump, trying to wrap this up today. thanks

[Mike C]

All of the big block parts are different except the pedal assembly. Engine mounts, bellhousing mounts, bellcrank, pushrod for the pedal and the pushrod for the throwout fork. You might be able to put the big block on the small block stands and have it work, but I think valve cover interference with the firewall is a problem. I think the 6 cylinder mounts are different from the small V8 mounts.

I bought all these parts years ago from a truck being parted out to convert my 402/TH400 truck to 4 speed. They are out there, but not that easy to find.

[wbc409]

I would put a wanted add in for big block motor mounts. Someone on the forum should have set they are willing to part with. There should already be holes in the frame to move the transmission cross member. Even with the correct mounts a big block is a tight fit against the firewall.

[Mike C]

The SM 465 does not have a rear trans mount. It has the forward mounts that attach to the bellhousing. Thus it needs the big block only SM465 parts which are different than the small block parts. And because it is moved forward for firewall clearance, the pushrods for the clutch linkage need to be longer as well.

[along for the ride]

How much different are the mounts and clutch parts if it is one of the GMC big block v6 engines and you wanted to do the same thing and put a big block v8 in on your four speed?