92f150300six, Yes the whole bottom end feels tight, the motor maybe has 25hrs on it from complete rebuild done maybe 2 months ago.
** Little history of my blasty **
Cases replaced also as the old ones had a huge hole the size of a medium orange in the bottom directly under the crank where the previous owner had busted a piston skirt and it found its way out the bottom sadly. I purchased a set of good clean used cases from feebay for 88 shipped to my door with transmission included. I purchased a wiseco stock stroke crank,rod,piston,rings,bearings,gasket set as a complete kit from feebay also for a pinch over 200 to my front door. The cylinder I had brought to a local machinist who did the boring work on my chevy 350 ( I know it may not be the same as a 2 stroke cylinder, but he did an amazing job on the block of my truck ), $50 for the overbore and free chamfering.
I followed Ken O Conners engine assembly vids when putting her back together, and even had the man on the phone after I encountered some problems out the gate which turned out to be a fuel delivery issue(petcock partially plugged ) thanks again btw ken if you ever read this. I am also leaning towards a casting flaw as the explanation for the odd looking head damage, as both you and scottj77 have suggested.