This is a Bosh Colt Spindle Mount for Shapeoko 2 Made to be reinforced with a Ubolt
My Shapeoko 2 has been in pieces in the middle of an upgrade and I forgot to take a picture of it installed. I don't know when I'll get back to it so I was posting this here for posterity.
If you think it is close to something you can use here it is on tinkercad. https://tinkercad.com/things/8ih9GRJED0h
Print out the bracket and clip a 3/8 x 3 1/2 x 5 1/4 ubolt around it. You may have to experiment with mounting it. I cut holes that mapped directly to the shapeoko mounting bracket.
I am posting this to share the idea as I'm not convinced the design is perfected but It seemed to be reasonably rigid in a couple of trials. Your mileage may vary.