https://m.imgur.com/a/IySXv9S is the link to pics.
He could measure the distance of the posts from the drop outs, if it's the same in back as front then it's cantis all over. If not then you got an exotic on back.
Seems like nut vs bolt, though unusual shouldn't be a problem, just get a nut. Do the front brakes fit on back, if so you could look for some on ebay.