I would think your numbers would be higher also. .63 is a little small. It's likely restricting your power on the high end. Is your power band falling off at about 5400 or so? I made my numbers on pump gas at 12 lbs with a stock cobra motor (with an F cam). You should be higher than me for sure. Was that on a Dyno jet or Mustang dyno? Mine was on a dyno jet. Mustang dynos are generally lower (and more accurate I'm told), but I'd think you'd still be higher.
I suppose there are too many variables to really decide where you'd be without knowing much about the car.
As long as your exhaust leak isn't causing your boost to fall off, your power output wouldn't be affected. You crossover tube, while small and crimped, should still flow enough to make lots of power. I've seen some small, real small, crossover tubes make lots of power.
Only expressing my oppinion here.
85 ASC McLaren Capri
79 Pace Car