Joined: Nov 2016
I can't speak to Galaxies, but on Mustangs and Cougars of this vintage, the MB version has a different mounting point for the brake rod. It's higher, closer to the pivot, allowing greater leverage, at the expense of more travel. The power brake version mounts the brake rod lower, and requires a pedal change for factory brakes. I suppose the reason for the change is to allow better modulation of the brakes, since they're more sensitive.
In fact, with factory brakes, if you use a manual pedal with a PB booster, you will put the rod at such a steep angle that it will bind or break things.