After all that, you might want to consider hiring somebody to do the tilling with their equipment. Might be a couple hundred, but the risk to your tractor is eliminated.
Now, if you do rent, raise your 3PH so the tractor and implement PTO stub shaft are level (this will be the shortest length of the drive. Then lift the PTO driveshaft yoke to see if it will the proper length without damaging your tractor. I like about 1" clearance
Buying a PTO driveshaft...well, IMHO, that's not a good idea. As an example, my
chipper's driveshaft is pretty short. My snow blower and flail mower drive shafts are much longer...depends on where the implement gearbox is mounted