@Stan Galat wrote- "...Stock, they came with metal discs and clutches, but there is a guy (Paul Guard) who has a rebuild kit available for them using friction discs and some other special whatnot. The mystery is if what I have will be rebuildable, as not all are..."
If the housing has worn from tabs on the plates (the only place they really wear), I have heard Paul doesn't feel they are worth putting the effort into, and says 1 day he will machine some new housings. Bruce (here in Burnaby- who I think sold it to you?) has reconditioned diff housings by welding/re-machining and can rebuild it for you with the Guard ceramic friction plates and proper belleville washers (he keeps them in stock). He will rebuild it for you.
Or- if you want to believe Mr. Guard when he tells you it is junk- instead of throwing it the scrap pile you can send it to me. I'll pay the shipping and a 6 pack (what the heck, make it a 12 pack!) of your choice.
Your Kanucklehead buddy Yoda
PS- ZF limited slip differentials were a factory option in Beetles and Super Beetles, various commercial vehicles, Karmann Ghias, Type 3's and Things starting in the mid '60's. There are both swingaxle and irs versions, as well as various later bus models. The thing- it seems they were never available in any cars destined for the U.S. or Canadian markets, hence Stan's comment that they are "as rare as hen's teeth".
I have no idea how accurate this code list is-