While cleaning up my X3, I noticed the flange installed in the rear
of the head. Why is it there? It would make sense if the head rotated on
it. Perhaps Sieg is using the same casting for the X3 and Super X3, and
maybe there is a way to adapt the X3 to a tilting head...

Look at part # 33 in the Grizzly user's manual. About a 1/2 inch bore.

R8 collet looks a bit crude. There were green paint flecks on the mating
surfaces.

I see no way to apply oil to the spindle. Is this so?