Opinion on engine condition after tear down

That top end definitely has some hours on it, but doesn't look bad - looks like an OE "B" piston.

A quick way to check the "big end" bearing is to try to snatch up on the connecting rod while
holding the crankshaft still. If you feel (or hear) any up and down movement, the bearing needs
to be replaced.

Personally, I would never race/ride a used MXer without tearing the engine down to the cases and
rebuilding it with new parts to replace anything out of spec. This resets the engine clock for the top
and bottom end as well as gives me a look to see what's what inside.

If you are comfortable not doing that, mic the cylinder to check in spec and carefully examine the bore
for any gouges or scratches. If it all checks out, run a hone through it to get a fresh cross hatch.
Replace the rest of the top end components with new, button it up and have fun.

dogger

Get a factory manual for all the tolerances and how to check them. You may need to find a good shop to mic your cylinder like dogger said.

the plating is starting to wear around the exhaust port ,but if you keep on top of the filter maintenance it will last a few more yrs. also the small scratches you see on piston i would say came from when the rod went out and they didnt get it good and clean before ptting it back together . i would ride the crap out of it ...

That topend needs rebuilt! I had an 05 kx 250 that never looked that bad, that's becuz I replaced my topend 2-3 times a year, depending on how much I raced.
But the good news is its a 2 stroke andaa new topend will have it running great again and it's cheap and easy to do.
My kx was an excellent bike and I know yours is too..
Long live the 2 stroke.