If you have the stock base model 3.5:1 booster, then you have to upgrade to the Sedan (1.5L, 1.6L) and Turbo (1.6T) disc brake boosters, that have 4.0:1 ratios.
Also, if you do not have the matching size of master cylinder for the brakes to go with the larger piston calipers or even dual piston, the brakes will not be working efficiently and properly, thus increasing effort and increasing the pedal travel.
Rear axles are the same between a turbo car and a non-turbo car EXCEPT for the tab where the parking brake cable intersection the axle. You can weld in one fairly easy. Galant's must be pretty darn similar, because they have the same rear calipers. If DSM brake cables work, why not the Galant?