I have now bought a 50:1 harmonic to play with, eBay item number: 291926642351
I thought maybe connect it to a shaft using my favorite Myford change wheels. Not easy to cut the middle out 100% concentric so I would have to spring two together, that seems to do the trick if you want low backlash with Myford wheels. I think I could enjoy this. Somewhere in my junk boxes I have a new pair of 40mm self-aligning, flange bearings, featuring grub screws on the extended inner race. They could easily become a part of this.