I have a 1969 toyota landcruiser i have replaced the master brake cylinder 3 times

might want to check your brake lines and wheel cylinders what are in your drums or get some clamps and put them on the rubber brake lines

Did you try adjusting all the brakes, They have dual adjusters on each wheel, you have to adjust primary and secondary shoes untill the wheel is tight and back off each one just a little untill the wheel has a very slight drag, it's time consuming but the pedal should come up,just make sure the adjusters are free and well lubricated