Well, the answer to this is "no".
No matter how I adjust the brakes and the hydro arm , there doesn't seem to be any noticeable change in the position the hydro returns to after full application of the brake. This is not good.
Applying the brake while the hydro is in reverse does return the hydro to the Neutral position, but that doesn't happen when the hydro is placed in the Forward position.
There's also a condition I've seen on two 123's , where the brake pedal , if not adjusted so that it's pretty sensitive to pedal pressure seems to go so far to the "floor" that the spring won't return it nor is it easy for the hydro arm to return to neutral. It's not the condition you want when it's time to stop. There's a "click" feel as if it's gone over center somewhere but I can't see it when I'm contemplating things lying under the tractor.
(UPDATE: I see where that "over center" feeling comes from. When the pin on the hydro handle mechanism clears the bevel on the ramp part of the complicated hydro control mechanism WAAAAY up there in the dash tower, I see why the pedal sticks and doesn't return. My guess is, that the brake action should never cause the pin to ride over the edge of the beveled part.
Maybe...)
There does seem to be 50 yrs of slop in hydro control shaft to the hydro control plate that might not be helpful.
Anyone seen such things on other tractors?