I had the exact same overheating problem with my 283. After 2 years of fighting with it, found out it was the thermostat housing. I had one of neat looking chrome ones with an O-ring. Took the O-ring out and used a gasket. The problem was it wouldn't seal. Replaced the housing with an original 283 one I got at a swap meet for $1 and my problem was solved! It's the simple things that getcha.
