Wow. Quite a list of things done and checked!! The head gaskets are easy to spot if backwards. If installed correctly you should see a square shape sticking out of the front on both sides. I also see more guys having these problems even with GOOD replacement parts. I've heard pros and cons about aluminum vs brass rads. Also that recored rads don't cool as well. I don't know. My Cougar has a 390 and the stock rad still and runs really cool at idle and in traffic so far. Are you using a surge/puke tank? BTW sounds like a REAL nice car and to me it's a HotRod!!