I have a n '84 B250 with a 3psd AT. I'd like to replace it with a 4 spd.
Is this possible? I don't know all the interchanges between trannies.
I know that the 4spd's didn't come standard until about '89. Any info and
suggestions would be aprreciated.

Read up on it here.
http://www.transmissioncenter.net/SwapInformation.htm