rings were washed out or incorrect gap, oil control ring isnt doing its job from the looks of burned oil remains between top and second rings, as for eaten away top ring land thats is from severe detonation poor fuel piss poor tune, not enough fuel too far advanced timing, im sure your top of pistons look like salt/ pepper and pitting. As for oil squirters, piss poor building, wrong pistons, or pistons facing wrong way. walls look ok, but always possibility that it is out of round from a diy hone job, have a respectable machine shop build the engine.