Two things about plugs that don't work well in our engines. Platinum plugs and Bosch plugs, for some reason they have a short life span in our motors. I'd suggest swapping them out.
The pistons may be chipped due to the low octane and continued predetonation that was happening. Borescope is likely the only way to tell for sure.
The belt missing means (accessory belt since you lost ps) you may have overheated the motor. Did you notice the temp gauge or anything dinging at you?
When you say won't start, do you mean it won't turn the engine over or the engine turns over and won't start? Possibly got your accessory belt wrapped up behind the harmonic balancer and it's binding things up.
