For a car application,stay away from the RV and 4wd casings. Most have a short or no tailstock at all.

Any B/RB 727 from 66 and newer are acceptable as cores for rebuild.
They have the slip yoke and rod actuated shifting (cable shift 65 and older).

Since you are going to rebuild the trans,you can install the part throttle 3-2 kickdown feature from any /6 or any 904/727 trans from the 70's-up
Use quality parts for the rebuild.
Be sure to match the convertor to your choice of cam and rear gears.
Hemi 727's came with 4 clutch bands,others had 3,so never hurts to throw an extra one in--again depending on what you are using the car for.

Another trick is install the lower first gear ratio from the 80's 999 trans found in 5TH Ave's and Diplomats for the quick take off in first gear.

The column or floor shift features are bolt on and not like the 4speed tailstock.

Others may chime in to add.
Hope this helps.