Looks like I'll be getting an LSD from a Z32 (90+) non-turbo Z installed in a couple of months. It's a viscous unit rather than a pure clutch type, and I'm hoping it characteristics lend itself well to off-road use. The Z31 unit has a cam mechanism in it that tightens the clutch pack under load. The Z32 viscous unit also has a clutch pack but does not have the cam mechanism. Instead it uses a special additive to the fluid that reacts to wheelspin (and the resulting friction/heat in the fluid) to make the clutch pack respond.
My gut has been telling me that this isn't ideal for off-road for a while, but the more I think about it it might actually do nicely. The price I got the LSD makes it worth a shot.

Brent