The important issue here is what engine do you have? A 216,235,261 engine has no provision to mount a late model transmission. This leaves you with a small choice of automatic transmissions to use. If useing a standard trans. you have a number of choices. The t5 seems to be the prefered trans.that most people switch to, 4 gears plus overdrive. The other issue you will need to deal with is your rearend,is it open( has a drive shaft that you can remove) or closed ( with a torque tube). If it is open you can put just about anything in, however with the closed drivshaft you are pretty much limited to what you already have.
