If you want the hand's clean method, find a truck drive line specialty shop in your area. When I needed to buy some longer PTO shaft parts, I took the part only to the store.
They had all the right pto sizes, u joints, etc and could have redone the whole thing while I waited, had I taken the whole thing in.
If you mount the tiller and do some measurements with the 3PH all the way up and all the way down (be sure to account for it being 6-8" deep), then take the parts to a shop, they should be able to build it for you.
My shop sold me a drop off piece for $20--had I found it at TSC, which didn't have it, I would have had to pay $60 to buy a whole 4ft section.
Hope this helps.
ron