Remove floor boards.
Loosen locknut on adjustment bolt out of brake housing.
Turn inside nut to right until you have about 1-1.5" free play on pedal. (I try to get both my pedals pretty close to the same freeplay so when I push both and rock my foot I get more or less equal braking on both sides.)
Retighten lock nut. (lock nut and adjusting nut are two different sizes)
Replace floor boards.
500b/600b brake set up same as early 530/630 tractors. Change made in 1961 or 1962 I believe. 500b/600b and early 530/630 is two disks. New system is disk plus band.