I figured I'd start posting today...
Before the server was reset, many points were brought up to this discussion.
1) The idea of relocating the engine closer to the firewall and lower to the ground was suggested due to the fact the removal of the front axles was now permitted if one were to convert to RWD.
A lower CoG and better weight distribution make for a better handling vehicle. The problem we run into when trying to relocate the engine is the fact that the subframe will not clear the current oil-pan as the stock oil-pan already sits pretty low. First, one would have to fabricate either a new subframe or a dry sump system, perhaps, in the worst case scenerio, both of these items might need to be custom fabricated.
Assuming that one decides to go this route and fabricates a new subframe and/or a dry sump system, the next potential problem would be the engine accessories and all those other items cluttered in the engine bay. With the engine in a new position, all these other items might need to be removed or relocated. For instance, a battery relocation to the trunk. (although the battery would not be something that would need attention)
Another problem that comes with engine relocation is the fact your off the shelf turbo kit, intercooler kit, intake, headers, etc, may no longer fit. The diameter of the pipes may be incorrect for the new engine position, headers may not clear certain accessories, etc. In conclusion, engine relocation may open up a can of worms RWD Subaru enthusiasts are not ready for.
2) The rear differential was confirmed as a dire problem needing a solution. The stock R160 will not hold for anything more than some spirited driving. A new differential would definitely be needed.
Some people suggested running an R200. The R200's are easily found in some late model Nissan's as well as a few other cars. These rear-ends can be picked up at a local junkyard for under 1000 dollars, however, there are no off the shelf axles or mounting kits that will allow you to simply bolt on an R200. The heavier R200 would also help weight distribution by bringing more weight to the rear of the vehicle.
A much more feasable rear-end solution would be the R180 already found in some JDM models of Subarus. These rear-ends have been bolted onto numerous USDM Subaru cars without much hassle for quite some time now. The swap is well-documented and should prove to be a better alternative in a solution to finding a rear-end that can handle the added stress.
3) Many people who have already converted their cars into RWD have experienced a similar outcome when stepping on the gas pedal - wheel spin.. lots of it. Getting power to the ground is a problem.
Subarus were designed from the ground up as AWD cars, some of them were designed to also be FWD. Subaru, to my knowledge, has not built a RWD vehicle. All the research and development that went into our car, especially the suspension geometry, was meant for an AWD vehicle. Turning a Subaru into RWD means that the R&D already done will no longer suffice. The suspension geometry and suspension parts are no longer suited for the new driveline.
AWD cars and FWD cars handle quite similarly, however, RWD cars do not. The handling dynamics are vastly more different than AWD/FWD therefore, our average off the shelf coilovers, as well as other suspension parts, may not actually be much of an "upgrade". The spring rates on these coilovers are inappropriate for a RWD car, therefore, RWD-specific coilovers have been suggested as a solution for getting power to the ground as well as help with the car's new handling characteristics. Custom sway bars are also another good solution, fortunately, Gruppe-S has already created their own sway bars which they also happen to use on their competition drift STi.
Last but not least, a proper suspension alignment should be able to set the RWD Subaru off just right. With the proper tuning in toe, caster, and camber, the car should behave decently, if not well.
4) Most Subaru transmissions will not be able to handle the added stress associated with running high power numbers through the rear wheels. It was suggested that perhaps a proper RWD transmission could be used in conjunction with our boxer through the addition of an adapter plate.
There are many RWD transmissions out there that are strong enough to handle the stress in a built RWD Subaru. For instance, the R154 from the MKIII Supra can hold up to around 700 horsepower and can be found for around 1,000 dollars. Quite cheap for its potency. Other notable RWD transmissions include the T56, which comes in many GM-model performance cars that come with an LS series engine. These transmissions are close to bullet-proof and can handle quite a lot of power. The transmissions that come in the 300ZX Turbo as well as the 350Z/G35 should also be considered. These transmission will be able to handle more power than a rebuilt 6-speed Subaru unit as well as being much, much cheaper.
There are currently no RWD Subaru's running around with a non-Subaru RWD transmission. There are many advantages with running a RWD specific transmission but there are currently no flywheel combos discovered/adapter plates created in order to mate any of the above listed transmissions (or any other RWD transmissions for that matter), into a boxer engine.