I have run a 7 lbs cap on my 47-54 truck radiator for over a decade daily. Also with a late 235.
I believe the pressure limit has more to do with how much the radiator core can handle.
A few years ago I recored the radiator with a 3 core.
Higher coolant pressure increases the boiling point.
A higher pressure cap may cause more leaks on an old radiator core than a lower pressure cap and the hoses may need replacing sooner as well.
