I have no idea on the phantom thing, never herd of one of them before.
My current dirrection of thought on a locker though is to swap out the rear center section for somthing else that is commonly available, cheap, and has lockers available for it.
So far I am looking into a ford 8.8" front center section from an exploder, or the rear center from an independant rear toyota celica they to fit the above criteria fairly well.
I need to look more into the stub shaft issue though, the fords come stock with a stub shaft with a u-joint yolk. Would also need to fab up a mounting plate, that should be no big deal.
The only other problem I see so far would be the overall width, from the ends of the stubs being too wide. might need to look into adding a little width to the rear track to be able to use stock subaru axles.
Might look into using a diferent cv axel too...
That's not an 8.8, it's a Dana 35HP, and it's a tuff little diff. in the front, but with it being an HP diff. I'm not sure how well it would hold up in the rear.
U can find 'em in the rear of somthing, Corvets I think, but not sure on that. I might be wrong, but I think the R200 would be a better, and eazyer choise. And U can get an air locker for 'em 2.