i am in a similiar situation w/ a 46 1/2 ton and a dead 216 '50 sedan motor. the 235 swaps out all they way until 62 i believe. from the guys at patricks i was told that an early 60's saginaw 4 speed is a direct bolt in and thay have a torque tube conversion piece to swap out the sag tail and keep your torque tube in line. i was also told that patricks has a 3:55 swap for the original rear.
if the 235 i am looking at works out i am going to have some decent rebuildable 216 top end parts and other stuff. if needed let me know

"it's only old if you can't find a use for it; otherwise it's cool and i'll use it."