Running hot, I think.....

I would first put a proper water temperature gauge on there to see what the temperature actually is. The stock gauge is just an indicator and sometimes isn't working correctly after 40 years of service.

If you want to check it on the cheap I'd put a new radiator cap on it that has a little temp gauge built in. You could also check the temp with a Infra-red temperature gun if you have one, just point it at the top and bottom rad hoses to see what temp you are running.