My belt drive backer came in! After overlaying it on the one I removed from the parts chassis, it was even more obvious that it was bent.
I thought I had a good Quickdrive jackshaft, but after closer inspection it turns out that the bearing race where it goes through the backer plate was bad.
New ones are close to $400 (and even still spendy at cost), so I scrounged up a chaincase one for free and decided to turn it down into a Quickdrive one. Made a quicky marker with a hose clamp to see how doable this will be.
Chucked it up in the lathe. Already did a rough cut on the tip with a death wheel to get it close to where it needs to be. Faced the end of it to the correct length.
Turned in the factory taper on the splines. Made the angle slightly higher than what the factory did to make it a little easier to slide the sprocket on during belt changes.
Drilled a pilot hole and stepped up to the first bit to thread the end.
Tapped the end to M10x1.25, added a slight bevel to help guide the bolt.
Side by side to the factory Quickdrive shaft.
Just had to assemble it on the floor!