If those pistons had .004 side clearance, the engine was assembled wrong. those should have around .0015 Detonation usually starts to lift the edges of the ring lands, similar to your photos. Since you don't know the whole story behind the damage to this engine, why trash KB pistons? I have used them over the years many many times with great results. Engine overheating, excessive ignition timing, poor fuel, etc. etc. could all be factors. Maybe a forged piston would have taken the stress better, no doubt, But I got a couple forged pistons on my shelf with lifted ring lands, do I blame the piston company? Nope I blame the failed fuel pressure regulator that was the root cause of the failure.