For the rear diff, it's popular to source an EVO 8/9 factory LSD which is a clutch type diff, far superior to viscous. All you need are the inner cups from EVO rear axles, just install those on your existing axles, and everything works with your existing ring and pinion and diff housing. I'm planning on doing this with my car someday, I even bought a LSD and the axle cups already. There are a few write-ups on the forums about it as well. TRE can also re-stack the clutches to make it more aggressive if you want.
