Found my dads original 1971 duster!

Someone said earlier that too much timing will make it run hot. That's incorrect. Not enough timing makes one run hotter. Where is your initial timing? If it's too low, you start the burn late and it's still burning coming out of the engine and produces more heat.

That might have been me, I know I made a comment about timing.

That could be your whole entire problem! You need to pull that timing up to around 16-18 idle timing instead of 4. 4 is ridiculous.

Wasn't the factory spec 8 BTDC? I run 16 so not arguing with your suggestion.