You will need to use a beefy trans, like a Tremec TKO-II for a big-block car.
You will need to get a toploader bell housing to bolt up to. Trucks are a good place to find one of these.
You can get the adapter plate from many of the online sources.
The shop I use put a TKO behind a 390 not too long ago. You might call them and pick their brains. Mustang Fever, 408-748-1337. Ask for Mitch and tell him that I suggested you call.