If you run the T2 diff, you'll need to swap over the front section of your miata diff so that it will bolt up to the PPF. However, I think you'll need a 1.8L housing to accommodate the T2, as it's a 7 or 8 inch ring gear vs. the 6inch ring gear in the 1.6L diff.

Found this online:

"the TII diff is a big undertaking, however....the non-turbo LSD is not.

straight from my FAQ:

84-91 RX7 Non-Turbo Clutch Type LSDs can also fit into the 1.8 gear ring if you're looking for a good LSD as well. Clutch-types have proven superior in Drag and Road course situations as the lock under driveshaft torque, whereas a Torsen should prove better in an autox situation as it locks only when one wheel loses torque...so in the middle of corners.

The 84-85 GSL is a 3.909.

The 84-85 GSL-SE is 4.08.

You can do this conversion by two ways:

1. 1.8 open converted to RX7 LSD:

Parts:
94-05 1.8 Miata open assembly
84-91 NON-TURBO Rx7 clutch-type lsd (89-91 is a viscous, don't bother)
94-95 Miata stub shafts or 86-88 RX7 stub shafts and 94-95 Miata half-shafts
or 96-05 Miata axles (no stubs needed)
94-05 Miata driveshaft
Miata Ring and Pinion

Procedure:
Open the 1.8 miata & pull the open diff. Bolt the miata ring gear to the RX7 LSD. Drop it in, set the backlash and reassemble the housing. Swap/install as normal.

2. 86-88 RX7 assembly conversion:

Parts:
86-88 RX7 NON-TURBO differential assembly
94-95 Miata stub shafts or RX7 stub shafts and 94-95 Miata half-shafts
or 96-05 Miata axles (no stubs needed)
94-05 Miata driveshaft
Miata Ring and Pinion
Miata Pinion housing (pumpkin) (find at RX7 performance shops)
Miata Diff. Bushings

Procedure:
Open the RX7 assembly. Bolt the miata ring gear to the RX7 LSD. Swap the LSD to the miata pinion housing. Set the backlash and assemble the miata pinion housing to the RX7 carrier. Drill out the RX7 diff bushings and push in miata specific bushings. Install as normal.

*note: The 85-85 LSD will fit, however, the housing is not compatible....unless you want to convert to a solid rear axle
**note: The 89-91 Non-Turbo LSD will also fit, but shy away from these are they are Viscous LSD units and aren't worth the trouble.
***note: Replace the (2) seals on the Diff before reinstallation (MA02-27-238A $5.95)"