Some of the older John Deer lawn tractors, and some others had what they called a "Duo Trac" option. Most of the ones I seen came in the 2 speed hydro models. The manual I have ( I think it has the part numbers in it to ).
The million dollar question is " can one still get all the parts " to put one together. One part not available, and the hole deal is off. Knowing Peerless, hit the bank and remortgage your house.
At the age of these tractors that HAD them in and the junking frenzy a few years back ( I seen things get junked that there was not a thing
wrong ).