The new Wolfgang Engineering TB-650 is now mounted up to my Zenbot Mini. I got tired of waiting for Zenbot to make and send me the right mounting plate, so I took things into my own hands. I just removed the existing Z-axis plate, and drilled the 1" x 1" hole pattern into the front that matchs up with the aluminum mounting plate that came with the new spindle. The whole thing is about 0.5" out further than is needs to be since I have both mounting plates screwed together, but for now, it's on there and looks pretty good. If at some point I need that extra 0.5" back on my X-axis travel, I can look into something better later.
I ordered the SMD electronics from Mouser, so those should be here in a few days.
I have been continuing to wrap my brain around how to mill a double sided PCB still. The whole side-to-side registration operation is probably more simple than it seems, but I think I have a strategy worked out. I just won't know until I try.
New spindle mounted: