help with fouling plug

I might look at the carb throats that feed that side for a fuel drip. IIRC, the rear carb venturi sits almost on top of the #8 port. That's the first one I would look at for dripping.

There are some idle mix adjustment screws in the baseplates of the outboard carbs. If somehow those got out of calibration, especially the rear carb, it could cause issues. Does #5 plug look wetter than #7? If you don't have them exposed so you can adjust them, might be something to consider.

There is a nice 6 pack tuning guide on moparts in the tech section.