Milling head/spindle completed
The milling head is assembled and ready to be attached to the column. The pictures below show the parts. Just the frame, a collet holder, the pulley, and two bearings. The bearings are just radial ball bearings. I thought about using angular contact bearings, but the local bearing supplier recommended these ones. Since the intended use will not exert any axial forces, I hope they will be sufficient. If not, I will replace them with more suitable ones.
And this is the vise that the milling head will be mounted to. I have no idea what it was originally used for, but it is extremely well made to close tolerances.

Top view of vise. The milling head will be attached to the moving jaw (the large flat surface on the right).