Timing Curve on 360 in an RV

78DodgeRV said
Awesome, will give this a shot. Currently have vacuum advanced set to zero. Played around with 0-5 degrees of vac advance, but pulling it back to zero helped with backfiring. For some reason, anytime my timing started getting into high 20’s, I was getting backfiring.

I would put an old/another cap cut so you can check rotor phasing.
It sounds like your spark may be jumping around in the cap when the mechanical advances due to the rotor moving too far away from the terminals it should be firing to.
Check out my video on this: