It was more of an observation, but if that’s what you needed........I’m sure a factory 12” converter could be made to live behind a motor like that.

I’m also confident an 11” could be tightened up enough to stall below 4200.

68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads