on a 59, your SM420 will just have a yoke on the back, as Mike B, no park brake on it. Ed is right, best once the rest of the drivetrain is in and truck sitting properly, measure length between rear end and rear of trans (in between the centers of the u-joint yokes), like where the center of the u-joint cap would be) and get a new one made or find one in a wrecking yard or from a donor truck.
