Lockup to non-lockup question(s)

LU is lock up converter. If you're going to do over drive, you might as well go LU, also. If I remember right you have a small block engine. There is no REAL EASY way to do the OD/LU on a "A" body. The easiest trans to use would be the A-500/42RH trans. It will sorta bolt up to the LA engine and has OD and LU. However you will need to cut the floor and make a new trans crossmember/mount. Driveshaft will need to be modified. Then you will need to do the electrical controls for the trans. This can be as simple as two toggle switches, or as fancy as some pressure switches, vacuum switch, and relays, for automatic operation (kits are available). Might have to fab "kickdown" linkage.
There are threads on this site about doing this conversion.
I also know of some people that have used the GM 200R4 transmision. That can be done without cutting the floor, but requires many special parts (read much more expensive).
If you want to talk about this stuff, send me a message, and I'll give you my phone number