Not sure where you're measuring the free play, but in my 1936-1942 Plymouth service manual, page 77, says:
(1) "Free play in the brake pedal should be from 1/4"-3/8". This free play may be readily felt by hand and is the movement of the pedal before the push rod touches the master cylinder piston. If necessary, this free play may be altered by changing the length of the piston push rod."
"CAUTION:piston cup must clear port when pedal is in released position."
(2) "After the free play is taken up, and the pedal is pushed slowly for an additional 5/8"-3/4", fluid should be forced up through the relief port in the master cylinder. If it does not, and the free play is correct, the master cylinder should be disassembled and checked for swollen cups or improper assembly of parts. The additional pedal travel of approximately 1" is required to move the brake shoes outward against the brake drums."
This is verbatim, except where it references a couple of figures. All measurements are taken at the foot pedal pad.