I have not tracked that info down yet. My tower came out of a very old bar in Jersey somewhere. I've seen similar towers in my area but I find the guts are different - when I can talk the bar into letting me pop the top. I'll look into those washers you mentioned.
If I turn up any more...
Sounds like you are describing exactly what I am running into. Mine is a 5 tap but the shanks look to be 1/2 inch with the small tapered grommet on back. Added an image of the shanks in stages of disassembly.
The CHI link does not come near what I am looking for. Did you ever find...