The OP still hasn't answered the timing question. If it's too far retarded, it will definitely run hot. I've been a GTO freak for over 40 years, and have had a few. Some 455s. When all is right, it should run way under 200°. But if the blocked is punched out too much, (.060), and other problems exist, it'll give problems for sure. By it running hot in town, but cooling down on the hi-way, it sounds like a capacity problem...possibly. Or an inoperative fan. Hoefully he'll up-date, with his new radiator. The combo sounds like a fun street machine.
