Here's FAQ on spark-plugs:
https://faq.ninja250.org/wiki/Changi...rands_to_avoid
Unfortunately, someone put new-gen 08-12 plugs in your bike. Those have longer reach:
https://www.summitracing.com/search/...s?fr=part-type
Never trust parts-countre muppets, always verify part-# and measurements yourself.
If only parts that contacted was piston tops, I would think just just that and maybe con-rod would be all that's needed.
Look up posts by Mohawk, Racer X, and Bruce71198, they've all built upgraded engines have have some good specs on parts.