Well, I finally finished this a couple weeks ago and had a chance to test it by putting in some wildflower beds for my mom. It works great! None of the three belts slipped, and the engine doesn't even know the tiller is there. It's nice to be able to remove or install the tiller in about 5 minutes, which is possible since the gearbox stays attached to the tiller.
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Before I could use it I had to come up with a belt that would work, which is mostly why it's been a year between posts about this. The original belt for this application is NLA, and any suitable belt I found was very expensive. I decided to make a jackshaft to mount under the tractor so I could use the deck belt from my 50C, as well as the existing mule drive with the angled pulleys so I wouldn't need another mule drive. I had a couple of pulleys and heavy-duty flanged bearings around, and I made a keyed shaft for it. I then put together a structure to hold the bearings and pulleys, offsetting it about 2.5" to the left to match the angle of the mule drive pulleys, and then I was able to use an additional short, cheap ($21) belt back to the tiller. I added a tensioner borrowed from a 2000 series deck that I parted out. No additional holes were drilled in the tractor; all existing ones were used to mount the bearing/pulley assembly.
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