hole/melted piston

got the head off the new xj today, and whollaaa!! no wonder this cylinder only had 30psi! anybody know where i can find a good/cheap motor? i guess i could rebuild this one, but i would rather swap and have a third motor as a spare/stroker.

That´s a good reason, not to switch, to a hotter plug and run it at high RPM´s. That looks like a classic, to hot of a plug, burnt piston. If you got to stray from the recommended plug, hotter plug for short trip driving, recommended plug for all around and a colder plug for flat out, well beyond the speed limit, long runs. Seen the same type of burnt piston, many times here in Germany, there are no speed limits on the autobahn.