Have you checked your vacccuum advance diaphragm lately? It should run fine at 11B initial, assuming the damper hasn't slipped. I think I'd fatten it up a bunch to see if it helped. That's what others are saying when they say double-pumper, they just don't realize it. I had a '67 New Yorker with a similar combo and I had to fatten up the AVS I was using a ton, but then it ran great. At 4500lbs it ran 15-flat in the 1/4-mile and chirped the tires on the 1-2 shift. That was with a Performer intake, HP manifolds and full dual exhaust. The cam was similar to the factory HP.