I had the same problem on my set up. It's a Mustang m/c & booster with front & trar drums.
I found that on the lower brake pedal arm that goes back to the m/c, the length needs to be extended so that the hole where the rod to the m/c mounts is 1" below the original hole. That improves the leverage & shortens the pedal travel.
If you have a fax, I could send you a copy of the diagram I found.

1949 chev 3100 3 window. 350hp/327/m21 4 spd, 12 bolt rear, power brakes, 3" dropped axle from Sid's. Disc brakes next.