Again, I'm not saying build a buggy. Just build the best darn offroad Subaru anyone has seen.
If you're going to modify a subaru that much, where you have a divorced transfer case, custom built suspension, custom axles, and custom subframes front and rear there isn't anything "subaru" about it's offroad abilities. You could start with any passenger car, and get identical results. I would choose something with a strong lightweight unibody, a durable motor with lots of torque, and good rollover protection. Probably a Volvo 140 with a B20F engine, a mercedes W115 with an OM616 engine, or a 1.6l VW diesel 2 door wagon would be a better canidate than a Subaru. What's great about a subaru is that they are cheap, fuel efficient, handle like a car, and are reasonably good offroad. If you modify it like that, you lose all of those benefits except the offroad abilities.