I would recommend using as large a radiator and condenser as you can fit in. I would also recommend an electric fan, or dual fans so you can keep the high side pressure under control and the AC working when idling or stuck in traffic.
The Vintage air Gen IV Magnum has served me well for a number of years, very good unit.
I have a 65 LS truck but here is a link to my AC install that might give you some ideas.
http://67-72chevytrucks.com/vboard/s...d.php?t=468107
Good Luck, TR