I just acquired one of these in good shape and am getting it set up. It has
a hefty-looking 4-spur drive center in it right now, but came with 4 great
faceplates of varying sizes.

My problem is I can't figure out how one would remove the drive center. The
outboard end of the shaft has a long nut going into the [threaded] shaft,
but this just comes out and nothing happens. Similarly there are two small
set screws with allen heads outboard on the side of the shaft, but removal
of these accomplishes nothing either... The thread on the outboard end of
the shaft is smaller than the thread on the face plates.

The spur drive center has a large (1 1/8?) hex head but there is nothing to
turn against.

Help!!!