Is it a stock 6 cyl or modified V8? If it is a 6 you are running way too much pressure in the radiator. Get a stock (4-6 lbs I think) cap.

Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
‘65 Chevy Biscayne (Emily)
‘39 Dodge Business Coupe (Clarence)
“I fought the law and the law won" now I are a retired one!
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USAF 1965-1969 Weather Observation Tech (I got paid to look at the clouds)