I have the original 4 speed, it has a crossmember with a mount but I removed the mount because the rubber was gone and it leaks at the bell a bit.
However, the rear transmission mount doesn't seem to take any torque off the side mounts anyway.
I'm planning to drop a Jimmy 302 in it later this summer. I have two front mount options, the original style 2-bolt mount, and the saddle mount with a single bolt. I'm leaning toward modifying the front crossmember to accept the GMC mount rather than changing the engine front plate (which doesn't have the tab that the Chevy engine does). I haven't decided what to do with the rear mounts yet. I'm also switching to a Saginaw 4 speed so that may help with the rear situation a bit.
