Ok, I've replaced the MC, front calipers and added an ever stronger return spring but still having some issues. After a few stops the brakes "pump up a little" less pedal travel. If I stab the pedal hard the problem goes away. There's not as much brake drag as before but there's still more than I like.
A few months ago I did replace the original 7" dual booster with a new 8" dual booster, they're both the universal style with the same bolt pattern.
Anyone ever heard of a dual booster hanging up?