Blackfoot,
Sounds like you're pointed in the right direction now. Traction & gearing sound like your most important upgrades at this point. 3.73's should be a good compromise for the street while letting the 400 reach it's potential on the strip.
Sounds like you have the carb, intake and exhaust pretty well set up, but IMHO could stand a bit more cam than the 068.
14's are easilt in reach with a rear end & cam upgrade.
http://kurtspontiac.homestead.com/TimSimpson66GTO.html