I have 2 junk 2.5 engines, and wonder if any of the innards are re-usable.

One engine has stripped head bolt holes, and the other one has some cylinder wall scoring.

 

Pistons seem o.k. on both engines, are they usable in another engine.

I haven't split either engine, but I'm assuming the crank, and rods would be good too.

 

I hate the idea of junking parts that are still serviceable, and I seem to be gathering quite the collection.

I usually grab the sensors and stuff, then toss the blocks. If you want to keep other parts to rebuild stuff for yourself, go ahead. But blown up ej25's have nearly an infinite supply, and thus no real market..

Split them and start an aluminum scrap pile.  Find old wheels and other aluminum and when you get a good amount, it's worth it to take it down for scrap.