Tuning with jets, Power valves and an O2 guage

I see no mechanical reason why it would ping given the specs you list. Also - the fire ring deal - I would say the ring burnt as an affect, and replacing it with a larger bore dropped the compression enough to fix it. But that's a guess on my part.
What is the rpms where the centrifical advance starts and when does it end? With an advance light you should be able to find that out.
I'm with RAT on this - What I would suggest is you rethink the timing curve and use the 750 as the "base carb" for this as I trust a Holley far more than Demon to stay consistent. Drop the initial down to 12° and find a stiffer spring to slow the advance. You can also lighten the weights but I'd try to find a stock "light" spring from a factory stock type distributor. If you can't find any let me know and I can mail you one. I have some of them and some Mallory ones that might work too. I'd like to see the timing curve start from a lower number, and come in more slowly, like starting at 1500 and not coming all in until 3K. The "two light" springs start it early and it's all in early.