A 1951 235 engine would have originally been installed in front of a Powerglide automatic transmission. There was no 235/3 speed option from the factory. That engine is just sort of an upsized 216- - - -it still has the Babbit connecting rods and spray-oiling system with the dippers on the connecting rods. One big difference is hydraulic valve lifters on the 235. The 235 will be virtually a drop-in swap, as long as the front motor mount at the timing cover is there. Powerglide cars had a different mounting system- - - -side mounts on the engine, and one at the back of the transmission. If the engine you have is already running a 3 speed manual, it's probably been converted to the bellhousing mounts and the single point mount up front already. Adjusting the hydraulic lifters so they don't rattle can be a challenge, but the original equipment lifters from the 1950's are MUCH better than the brand new replacements that are available today. Have fun!
The car transmission is a light-duty unit that won't bolt up to the truck driveline properly. The trucks got a beefier transmission with a different bellhousing bolt pattern in 1948, IIRC.
Jerry
