this Stl-File is tought for 3D Printing, but of course milling from a aluminium block would be even better.
I use the Kress 1050 Spindle with a norm 43mm fitting. The 4 cylinders on the side fit into the three way cube corner connector from the OpenBuilds Part Store which then be fittet on a V-Slot 20x80. See picture
43mm Spindlemotor mount e.g. Kress 1050 Current Version Aug 2016
Z-Axis Spindlemotor Fitting