Is your pulley moving in and out of the tractor when you try to operate the clutch?
I ask because the '39 H was unique. ONLY the 39 had the driver disk fixed to the camshaft by a snap ring on straight splines. The 40 and up used tapered splines, a cap screw and heavy washer. Is it possible your snap ring is not in place therefore allowing the entire assembly to slide back and forth on the cam shaft as lost motion instead of operating the toggles and dogs to squeeze the driving disk?