Brake pedal is really stiff
Bleeding the system might be a good place to start. .
A hard pedal is the OPPOSITE of a bleeding problem.
Besides what's mentioned, the size of the master bore, there are a few other things----any chance some restriction in the system is stopping flow?
But the OTHER biggie---mentioned the other day---is the fit and quality of the shoes/ drums.
Cheap shoe lining can give poor braking performance
Drums that have worn/ or been turned too large cause poor performance, because only the center area of the shoe lining contacts the drum---the upper/ lower areas aren't doing anything to stop the car, and worse, the "overwork" on the center area of the lining causes it to quickly glaze and become WORSE
Drum wear--drums never wear evenly "flat inside" so that when you put nice new shoes into worn drums, they don't contact evenly across the WIDTH of the drum, causing the same thing mentioned above, but now we are speaking of (typically) the drum wears "dish" shaped ACROSS the drum, and the edges of the shoe tend to hit first.
Last, all the "big three" did the "same thing." On smaller, cheaper cars, with smaller engines--you always got the smaller brakes. You didn't mention what size they were, but if they are say, the little 9" brakes, they WON'T stop as well as "might be expected."
