Slant 6 Overheating

I just spent a few minutes checking the timing and dwell. Dwell was at 39 instead of the 41 to 46 - I don't think this is far enough out of spec to cause overheating. Timing was at TDC, and correct according to spec. Idle was a hair low, maybe just below 750.

Having seen a number of folks post that they advance the timing a bit, I tried 5* advance. That bumped the idle up to about 800, which I've seen posts use as a rule of thumb.

Took it for a 5 mile spin, stomped on it, had it up to 70mph and no pinging, good power. No dieseling when I shut it down, no boiling over. ?????

So even if I "fixed" the overheating issue, can someone please tell me why I would need to advance the timing to get it to run properly? Am I just masking another issue here that will bite me in the long run?

Thanks,

John