You are working with a 65-66 Kelsey Hayes, 4 piston calipers, aren't you.
It's been awhile since i got my hands on a pair of official 65-66 year, vintage, calipers, but i have rebuilt them.
I will be telling you to go online, and bring up all the vintage Mustang Restoration parts seller companies that come up when you bring up the search listing.
I know i got those items from some company, in the distant past, but can't remember which one(s)
Virginia Mustang comes to mind, for some reason or other, but i dunno.
Good luck.
Jim V.
hemi71x