Misfire at cruise, popping/afterfire at 3000RPM

Righty Tighty said
I started at 14 advanced, idle speed was around 850 IIRC, then revved until it stopped advancing, which was at 2800 RPM, and the advance was then at 24. New distributor from Summit. We had talked about changing springs to see if I could get more total advance, but the transmission took the front seat for a bit.

Edit: I was typing this response while you posted. I forgot I had a separate thread where we talked about that.
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Yep. Post 60 were my suggestions.
Assuming its a factory cam, initial is in the ballpark, from 900 to 2600 is way too late and from 3000 up is wayyy too late.
I think you have to expirment with the other springs and the 'limit' set somewhere around 18* rather than 10*. Because the limit also effects the initial spring tension, I'd make that change first.