I know you started off by saying you don't like gear types, but any way, look at OBX differentials. I don't know if they make something for the R180, but I did meet a guy who described having one in his 240, but not being a racecar it might have been an R200.

The 1987 1/2 to 1989 300zx turbos had a clutch LSD w/ a 3:74. 88 and 89 non turbo's got a 3:90 open. Both in the R200. The 3:74 clutch types tend to bring about $500 on the used market from what I've seen (and paid).

What is your aversion to the gear types?