Well I thought it was in a thread here how I went about building it.
I bought a generic 5” steel wheel, 2 piece.
Then I bought 2 generic sprocket flanges with 4 bolts.
I attached 1 sprocket flange to each side of the wheel. I attached the sprocket to one side of the wheel, then bought a generic brake rotor.
The hard part was making an adaptor plate to attach the rotor to the sprocket flange.
I mocked everything up with cardboard to make sure it was possible, and it was.
Then I brought the parts to a machine shop and they drilled the proper holes and it was pretty cheap. I did kind of Mickey Mouse it by using washers instead of making spacers but the bike stopped on a dime.
I’ll try to find my pictures of how I did it and post them for you