BBC Accel Gen7 tuning problem

[Denvervet]

I've got a GM 572 thats got annoying low rpm stumble that I can't seem to tune out. Background...stock single plane manifold drilled for EFI using 48lb injectors and accel throttle body that I think is about 1350cfm with one throat and two large blades.
Originally tuned with MPFI and a dual sync distributor but that one lasted only a few months before it went out and had same manners as when I changed out to batch fire and standard MSD distributor.
Ive to a TKO manual so able to cheat around the stumbling but getting tired of having to baby it. Pretty much up until about 2200 rpm it does this but accelerates just fine to redline. I had a accel tuner help me tuning while I drove about 2 yrs ago. He had to dump lots of fuel in and it did better (about 12 AFR). Problem with that is plugs get fouled pretty quick and and fuel scrubbing cylinders so oil gets dark fast. On top of that sitting at a light will about burn your eyes with unburned fuel.
I use this car just to cruise and play with ...not a track car.
Cam Specs 0.632/0.632-inch lift and 254°/264°

Question is where to go with this? I've leaned up the fuel map to make it not run as rich as well as played with timing and hasn't helped significantly. Do I need a different manifold, go back to MPFI so I can tune individual cylinders, live with it, or have to change to a cam with less duration ?