Does anyone know if a 13b lightweight flywheel will fit a 12a motor (as long as I use the correct counterweight)?

 

The 1983-1992 lightweight flywheel will fit 12A & 13B

 

There are only two flavors of N/A lightweight flywheel - 215mm and 225mm.

They all work with all engines' counterweights and they work with all N/A transmissions (save RX-8 which is Turbo size). You just need to get the proper clutch for them. 215mm flywheels are flat faced while 225mm have a stepped ring around the outside that the pressure plate bolts to.

Note: You will probably never see a 215mm lightweight flywheel anymore.

 

does that mean that it will fit a 12a from an SA?

 

Yes - it will fit. Just use the 225mm clutch and the engine specific counterweight.