Look for the parts required to install a period correct inline chevrolet six cylinder in a '55 Chevy. They all used the transverse engine mount that bolted to the front of the engine!! Fabricate a mid-plate for the rear of the engine to be bolted between the engine and transmission and weld on tabs to use the factory rubber mounts from a '55 Chevy. Finally, fabricate a crossmember to facilitate use of a transmission mount for the 700R4.
The engines in those tri-five cars mounted originally on four rubber biscuits attached to a transverse engine bracket at the front of the engine and on the bell housing. That configuration didn't support the use of modern aluminum cased automatics. The Powerglides, Hydramatics, and Dynaflows of the day were cast iron and didn't need the rear support. That 700 WILL!!
The Pontiac frame and the Chevy frame may be a little different. GM didn't start consistently using common platforms for another eight or ten years, but they'll be really close! The toughest part to find may be the front transverse mount. The rest will require some sheet steel, (I used 10ga for my mid plate) or 1/4" plate aluminum, (hard machine grade) and some steel tubing and maybe some angle for the trans mount.
This is NOT difficult to do!! I've done it in a one car garage with hand tools and access to a welding machine at a muffler shop!!
