Wow, interesting thread.
Most of us have been where DB started out, hellfired to make the most massively powered engine ever. We read everything and prepared to put every modification EVER into one engine rebuild. Sometimes it turned out ok, but usually on the road to progressive learning, mistakes were made. You cannot get thru a maze without a lot of wrong turns.
So, when something goes wrong, what to do? Lay out all the facts and learn from it so it doesn't happen again. You have to be honest with yourself and face the truth. Mistakes are the trailmarkers to knowledge. Face them and you'll be heading in the right direction. These days I do my experimenting one step at a time, and usually small steps at that. I really enjoyed JoeAK47's posts because he does the same thing, and it shows in his knowledge and reasoned approach here.
The marks on the sides of the bore could be polished sections from rings run in too softly or 4-square seize from a forge piston getting too tight. Pictures are not good enough to tell, but the bore crosshatch still looks great. Forged pistons will measure undersize at the skirt after a 4-square seize, also called a "cold seize" from running the engine hard while cold. That is why I hate forged pistons in these recreational engines. Too hard to stay off the throttle while waiting for warm up. I've scored a few myself, I know.
Poor DB, he was taking when he should have been listening. Replacing the piston and he could have been running again with his pride still intact and knowledge expanded.
Steve