It's been a long time since I've seen that avatar
I never get tired of watching it.
Trying to get Mike to modify that spur gear like sjcrss did in the first place would be great. And the shafts are pretty simple to make also. I made mine using 6 mm stainless steel rod bought at Fastenal.com. The modified spur gear and the two shafts from Mike with a materials list needed to complete the diff would be nice. The only thing difficult part to get is the output gear from the Traxxas center diff. They still don't sell it separately. I wonder if the 3984X output gear would work? I have one coming to study it.