My gramps was a moline dealer and the back tractor is a one of one serial number x he was supposed to destroy, so he put the other one on the front and used it plowing for 10 years in the 50s before anyone made 4wd tractors. He built 5 total 3 moline 1 ih and 1 deer. The original double header is the only one left. My dad bought it locked up and in bad shape for $9000 at his estate auction. I put trans fluid in the cylinders and soaked the valves then tapped each one, finally after 5 days I got it to turn over with a pry bar, turned on the propane and it purs on all 10 cylinders.
This one is hand clutch for both tractors so gramps ran cables and you have 2 throttles and 2 hand clutches. Usually leave front tractor in 2nd gear, then it you want to go in road gear you take off with the front engine then lock in the rear engine in forth, release front clutch and away you go. It's really cool for being built 60 some years ago.