Flutter below 2k rpm

I think it's too lean...I would shoot for closer to 12.5-12.9 at idle, and 13.2-13.4 cruise...try that. What is total timing? You should be no more than 34° total. I'm not a fan of using the Vac. advance...I would not use it if it were mine.
It's not too much compression for the iron heads....

Really ? 12.5 idle and 13.2 cruise. I thought that would be too rich. I will try it.
The timing is 19 initial + 14* mechinical
Vacuum has another 17 starting around 12” and all in around 17-18” ... hooked to ported supply.