Very cool! Love the work you're doing on it. The bitsa builds are right up my ally. I have some spare lst shocks but I don't think you would like the shipping from Oz.
Xtm did make a center diff upgrade but with a goofy 63t spur gear and planetary gears inside instead of spider gears. I have one, but the spur has been stripped and finding one is close to impossible.
I've been doing a lot of research and cross referencing and I think I'll be able to use spider Diffs out of the newer xtm xt2e. I have only found one report of the xt2e center diff and motor mount working on the xlb and all that was said was it works with a little modification....
So i measured the XTM xlb center diff and bearing to bearing it is 35mm, My spare mugen center diff is 32mm. If anyone has a extra center diff measure i'd greatly appreciate it. I cant find any specs on a XTM xt2e center diff yet.