I just bought an F1 Racing 11.7 lb CroMo flywheel
#9
Some of the flywheels will have the wrong thread 8x1.25mm instead of 8x1.0mm for the bolts that hold the pressure plate down. Just go to the hardware store and pick up new bolts. I would use some medium strength loctite too and possibly lockwashers if the factory uses em too.
#11
I don't think the pp bolts are actually that high of grade hardware- they only torque to 20ftlbs. and only need to manage the torque force of the springs and pedal/slave. Maybe you're thinking of the flywheel bolts? I know the bolts that came with my aluminum fidanza flywheel were nothing exceptional.
#14
The 1.6 and 1.8 Miata motors are internally balanced, which means the flywheel assembly (flywheel, pressure plate, friction disk) and the dampener are neutral balanced. In "theory", one should have the flywheel assembly neutral balanced as a unit when replacing/swapping parts. I'm kind of struggling with whether or not I should do this when I replace my 1.6 assembly with a 1.8 stock flywheel and an ACT clutch setup. I think I can get away without doing it (stock flywheel and ACT clutch "should" both be neutral balanced) but I'll probably price out the balancing too. I'd really hate to get everything buttoned back up and then discover some "new" engine/driveline vibration.