I agree with George in that the T20 discs only came as stock equipment on the Cheif and Thunderchief. By 1976 when the Superchief went into production, all the Attex machines came with the emergency brakes on the front axles. I think the guy selling the green machine on ebay was confused about the model (it's an ABS machine and to my knowledge all the Superchief models were HDPE).
The big discs stop you on a dime, but are on a common link with the pedal so they always work at the same time.
Don
Stuck in the seventies- not in the swamp.
(6) Attex, a Hustler, a Super Swamp Fox, (2) Tricarts, (3) Tri-sports, a Sno-co trike, 3 Dunecycles, and a Starcraft! ...so far