I have to say that looks like a lot of work for the end result but it looks like it would be reliable. When I did my 107 over last spring I upgraded my driveline as well as those couplers with the pin drive are a problem. I use my tractor for moldboard plowing, mowing. and snowblowing as well as other stuff. I put in a new driveshaft and coupler on the front side as well as a new rag joint about 4 years ago. When I redid it last year the coupler and the pin were already SHOT! Since it is stored in a shed that is cold over the winter where it is used the oil in the transmission is cold and makes it hard to start. I wanted a way to overcome this and to solve my driveline problems. To do both I put a clutch in it from a gear drive tractor. When I push the clutch/brake pedal it disengages the clutch and also returns the hydro lever to neutral at the same time. This got rid of the front coupler problem and as I have not had any real issues with the rag joint I left that at the rear. So far it works great.
I read your post several times to understand and get a picture in my mind...and I think I got it. So you have a 3 pin driver w/clutch and hanger to disengage the drive shaft that goes to the pump...to cold start your engine. And a good fix to your drive line. That is a new one to me. There was a Cubnut in east TN that had a 1806 CC, manual shift, yet it had hyd lift AND power steering. It was a engineering work of art. Once he removed the tunnel cover and you got to see how he did it, it looked beautiful!