2nd gen. RX7 Rear Differential Question

["Burns, James B." <BurnsJB1@central.SSD.JHUAPL.edu>]

What type of LSD came in the RX7 GTU 's' model?  I'm pretty sure the ratio
in that car is a 4.375:1, but was it a viscous or a clutch-type LSD?  Also,
in which model years did the GTUs exist?

Thanks,
Brad Burns