That really depends on what you are planning on with your car. If you are building it to bring to the track, then a manual setup would be ideal. If you are building it for a daily driver, then power would be the way to go. I think that a 2nd Gen (70-81 Camaro) setup will bolt right up for you too. If you do go that route look for a unit from a WS6 Trans-Am (The easiest way to tell a WS6 TA is that it will have been setup for rear disk brakes). That will give you the close ration steering box. Try and stay away from 79-81 models since the are metric you would need to get adaptors. altough the adaptors are cheap, it is just a pain to have to have them.
Hope this helps..