The subie R180 is identical to a Z r180 when it comes to mounting. The issues come when considering the axles, which are CV joints. This usually requires custom axles that still rely on the S30's stub axle, a major weak link imo.
The S12 already has CV shafts though, so I was thinking it might be possible to tear the subie axle apart and mate it with the S12 axles. There's also the R160 which is the same physical size, and ridiculously cheap, and will hold at least 300hp or so. The subie clutch r180 has proven to take well over 600hp with no signs of stress. They bombpoof.
The CLSD Z31 diff is hard to find anywhere, but I've been lucky enough to find a few. Sold them all though, needed the money more than I needed the part.