I am working on a 1941 chevy 216. it all started with overheating issue. I am connecting vacuum gage to line that comes from intake and goes to vacuum advance. disconnected tube from vacuum advance and connected vacuum gage. dont know the rpm. dont have a tach. doing by ear and vacuum. at idle when fully warm 15 inches is all i get. when i rev engine it goes above 20 inches.

ok to follow with this I am cleaning the block and radiator with vinegar. thinking i may have restriction in water ports. When I shut off engine radiator gurgles. Is this from exhaust leaking in to cooling system or do I have major air pocket?

Again any and all help appreciated.