I measured to get close... then I ended up pulling the pushrod out of the booster, gently setting the MC in place (keeping it square), then seeing how much farther in I could move the pushrod. Currently have it adjusted to zero, with no apparent brake dragging.

Apparently you're also supposed to be able to look in the master and see a poof of fluid when you press the brake pedal an inch or so if it's adjusted correctly (with everything bolted together).