I'll see what I've got in there, but I just want to avoid catastrophic gearbox failures as much as possible. I've heard good things about the JG stock motors, but as far as gears go I'm not convinced they'll handle the spring. If anything, I'd prefer that my gears are high quality so the piston is more likely to fail first.
As far as the piston goes, I'm mostly ordering that in case I screw up the AOE and sand down a tooth too much, I've got a few other parts in my cart for that purpose as well, like a spare tappet plate.