You have already told us that going from .025 IFR's to .028, and then to .031's the popping got better. I would suggest to keep the richer .065's in there and test the .033's. IAB's are easy to change so you can lean it out if it needs it. You have a good selection of IAB's to tune it.

You and I both run the FBO dizzy (setup for manifold vacuum = 30-32'ish degrees of timing at idle in D). This extra timing requires extra fuel to feed it on the idle/transition (IFR's/IAB's) circuit.
The first tuning change that I made after installing the FBO dizzy, was to richen up the idle circuit to make the A/F mixture richer at idle and low speed cruise (up to 50mph or so due to the vacuum advance too).