ZG1200 - he hogs out the stock C10 housing and installs the larger gear from the zg1200. You would also require the use of a milling machine.Thanks!
I don't know the particulars but shimming the bevel gear properly in the case is critical.That's a good point. I may gather the parts and see if a local differential shop is willing to dial in the gear lash. In the meantime I'll go with the taller rear and just mosey along on the trip.
Just for visibility, when doing pinion/ring gear interfaces, the automotive "standard" color is yellow. I've used it for doing automotive diffs and it works well. https://www.amazon.com/Richmond-Gear-5500011-Marking-Compound/dp/B000MISKMU/
Section 10 of the factory manual has a bunch of info on adjusting the final drive.
To the OP: I’m just curious. Why do you feelI always travel just a bit faster than the flow of traffic.
4500 RPM @ 75 MPH is “not good”?