Master cylinders are sized in relationship to caliper size and to a lesser extent brake booster power / manual brakes. With a stepped bore, front to rear brake balance can be altered by changing one bore size.

Many times the master cylinder pattern is the same across models or even across makes as auto makers generally use outside vendors ( Like ATE , Girling, Lucas, Bendix ) making swapping possible. Brake line location is usually different across models so some fab work will be needed. Early R129 cars have a master cylinder mounted valve that is somehow tied into the ABS, I've never researched it.

The real question is what problem are you trying to solve? Using a MC from a heavier car won't necessarily make the brakes work better.

If you are able to lock up the wheels / get the ABS to cycle under braking, the car has strong enough brakes. ( As long as there isn't a parts failure that causes only one wheel to lock )