I recently got myself a very good deal on a "China CNC". I was surprised it was not bad at all, especially for the price. Of course the 775 Motor is not the best choice for a spindle, so I got myself one of those 400W 52mm spindles.
In order to not need to disassemble the whole Z-Axis when swapping tool or motor, I made a design that uses 6 M3 screws with heatset inserts, and created a clamp for the 775 motor it came with, and a plate where I could screw the 52mm bracket for the new spindle. I'm planning to also design a penholder for this mount, so I can label the pcbs I'm milling with it later on.
You will either need 4mm M3 heatset thread inserts, or you can also use the provided cad-files to make the hole-size fit your needs. I have provided the original Fusion 360 file, as well as step and iges files and the obligatory STLs.