Okay, I'm getting back to this. Those 12 hour work days are killing my firebird time.

I replaced the radiator cap and checked the fluid. The boiling point on the fluid is 224 degrees.

I advanced the timing as you described, and the temperature rose to 220 degrees after about 20 mins of idling, at which point I shut it off. I think that rules out the main root cause being no vacuum advance? Though I’m sure it would help me to find one. I believe my Weiand intake doesn’t accept a factory vacuum advance distributor, so I’ll have to verify that.

I’ll read up more on the articles you guys have mentioned. Thanks for links. I don’t know for sure what the distance is between the impeller vanes and the backing plate. So that’s something I could look at.