[Jim A]

I have heard mixed reviews on Cardone distributors. They may make new ones, but are known for rebuilts.
I wonder if you got one with the wrong gear. It would be nice if the cam gear won the battle and the dist gear took all the damage.
I would take it back to AutoZone and lean on them some.

I won't argue about radiator caps and proper pressure, but I have run my '60 305A for over forty years and thousands of miles with a broken cap spring and NO pressure.
It runs nice and cool and has never overheated. The coolant sits an inch or two down and if I top it off, it will go right back down there and stay for several years.