The car really looks and sounds fantastic. Love it.

Do you have wideband?
If not, a gauge to eliminate the possibility of a lean condition could probably help figure it out.

I'm a far cry from professional tuner status however when I started working with the wideband I was suprised how
good the car ran, and how well it would go down the road with as lean as 17:1 a/f . But the temp gauge would always climb quick.

That's just one possible piece of the puzzle, though. Sorry for not answering the actual question, just wanted to mention there could be
alot of factors contributing to the problem. I haven't used vacuum advance in anything for some time now but I do
like to have it on daily driver type builds.