Hmm interesting thought, I have always heard that most carb stumble develop from NOT Enough initial time....... not to much. or am i miss understanding.
I'm 22 Initial and 38 total by 2800 rpm.
I kept the initial about the same. But I slowed down the advance . First got the one distributor so about 26* at 2200, 32* at 3700 and 35 around 3200 rpm.
Then worked on another distributor with chrysler advance to get a better shape. But with either curve, the flat spot and pinging is gone. This is street and autocross. I did have the car at the 1/4 mile once while still working on the advances and the carb. It was a bit of dog off the line at least in part 'cause I had taken too much out early in the curve (about same initial). Early curve I mean 900 - 1600 rpm.
Converter is a 17505. Was 3000 rpm brake stall , probably about 2700 rpm now.
I assume your set up with a lot more power, a higher stall, and lower gearing even though taller tires.
My gut is to try slowing the advance so timing from 2800 might be 30 - 32 and 38* is above stall.
Be interested to hear what others think who have messed with tighter converters and more load (taller tires or less gear).