heating issues when idling 340 73 duster

Totally agree. My electric fans are set to keep my 340 between 200 and 210.

I mean, the original thermostats opened at 195. Obviously modified engines are gonna be a little different, but water under pressure like it is in the cooling system doesn’t boil at 212. Even with only a 7 psi cap you’re talking about boiling at around 230* F. With a 16 psi cap like I run it’s more like 250* F.
Cooling system pressure increases the boiling point 3° per pound of pressure. 15# cap will get you 45° increase.