The distance across the stick to the tines of the swivel head is
1 and 1/32 "

The knob spins off, then there's a locking washer, another washer, then
a plastic bushing

The opening for the screw to go is 3/4 - 1/16 = 11/16 inchdiameter.
The end of the screw has a permanent plastic washer and the other end has a bushing.

The hole that goes through the head of the stick is lined with metal,
that in the very middle narrows to the diameter of the screw

I can't seem to remove this. So I can't slip off the swivel head either.

The screw is... a typical long screw and looks to be the same diameter as the screw on the quick release pad.
On the quick release pad is a Male Thread Size 1/4"-20 according to B&H.

More info at
http://www.thkphoto.com/products/slik/slik-13-2b.html
and from B&H
http://www.bhphotovideo.com/bnh/controller/home?O=Search&A=details&Q=&sku=48616&is=REG&addedTroughType=search