Hopefully you found your problem, but if not....

I was curious if you had checked your timing recently and if you had the vacuum advanced hooked to the manifold vacuum. Retarded timing could cause some extra heat, but since the only thing you've changed is the AC unit I doubt this would be the cause of your problem. Also, as someone else stated, if you haven't checked the clearance from the water pump impellors to the water pump baffle, that's worth a ton of extra cooling.