Lateral-g Forums - I know it"s HOT in Phoenix but....

I need some engine cooling help....
68 camaro, 468 bbc aluminum heads pretty mild street engine dynoed at 500 hp. I have a complete Vintage Air set up with the reverse rotation Steward pump and an aluminum 2 row (3/4 inch) radiator with twin 12' pulling fans.
I cannot keep from pegging the gauge at 250 degrees and boiling over when cruising for a short time in 80 degrees weather with or withour the a/c running. Tried different theromstats and none at all....no change. Timing is 38 degrees total, engine is not lean, and i'm out of things to try :willy: except a monster radiator. Before i do that....any other ideas???
Thanks, Bart