easy way to answer this is how deep are your pockets and how much cutting do you want to do
if you are talking manual trans i can help you with that auto trans no clue. i can tell you that you can use a 4 speed which is meant for the car. 5 speed i wouldnt do it unless you are going to have a fully built one to handle the tq. a lot of guys on our rx7 forum put 5 speed manuals behind high powered small blocks and LS1's and they blow them to pieces. A t56 out of a camaro/firebird/corvette with the LT1 motor in it will bolt on and be perfect because they are strong and have 2 over drives BUT you have to cut your trans tunnel like so
enjoy!!