If I read it correctly you're running a 4 lb cap. I would bump that up to a 7 lb cap since increasing pressure raises the boiling point of the coolant. Raising the pressure should theoretically keep the coolant from puking out due to boiling. I don't know what motor or radiator you're running though.
My 1951 F1
- Ol' Red
"No amount of planning will ever replace dumb luck"