What makes you think the engine "wants to vapor lock"?
As you say, "...after it's been running it seems not to boil water..." Water boils at 212F. Clearly your engine is running below the boiling point which is where it belongs on a zero pressure cooling system.
If it bothers you, install a recovery reservoir like a modern car so you can fill the radiator to the very top and monitor the coolant level when the engine is hot and cold.
1950 Chevrolet 3100 (Ol' Roy)
1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)
