s5 units will work, but they are VLSD and garbage. I swapped all 3 of my s5's vlsds for CTLSDI've been doing my own research on LSD's because I'm going to have one put into mine when I start driving it again. The LSD from S4 RX-7 turbos (1986-1988) should fit all 929's, FD's, and some miatas. The s4 turbo LSD is an 8 inch unit. I assume this is the same for the s5 rx-7 (1989-1991). FC gears don't fit the HC that one we all know for sure. So at the moment if you want to regear your HC you need to source gears from the HC. From the factory, USDM models got (3.7, 3.9) gears on the sereis 1 HC's. 3.7 on the manuals only and 3.9 on the autos only. I'm not sure about the USDM series 2 929 but most likely it's the same.
Someone should post all the gear and diff options for the were AUS and JDM Luce. I know nine2nine said his car has 4.1 gears. So gear wise that means we have three options available 3.7, 3.9, and 4.1
If I posted some any incorrect info some please correct me. This is just compiled info from notes I've taken while searching online. Also I'll have the info for what was available for the KDM Potentia.[/b]