Are you really saying that your -1 and SR heads made more power than B1/MC's? If so, something was very wrong.

I've dyno a bunch of different motors, street and strip as well as race only, all of them made better power with better heads
I tested two different sets of heads on two of my motors, one set of SR with M.W. ports that flowed 350 CFM at .700 on the intake side, one set of CNC ported 440-1 that flowed 370 CFM @ .700 on the intakes, both heads had 76.0 CC chambers. The SR made 727 HP on my 518 C.I. pump gas motor, the 440-1 made 775 HP using the same intake, carb, camshaft, ignition timing and pump gas.
The 526 C.I. bracket motor made 775 HP at 7000 RPM with the SR heads and it made 845 HP with the 440-1
I built one 543 C.I. B1 headed bracket motor and it made 920 HP on a different dyno in Boise, ID. Those heads flowed right at 420 CFM at .700,.800 and .900, the lift at the valves was.720
More air on most Mopar V8 = more HP usually

I hate to say this but if you had a big block mopar with B1 heads on it in a lite weight Dart and it only ran 6.20's I wouldn't tell anyone. I would put that info in the vault and lock it up. LOL. My buddy's Duster runs 5.80's with Edelbrock heads.