I'm with Arcticfriends on this one

The Damage Is On The Outside Of The Piston And The Cylinder Wall Is All Scored Up, No Damage To Center Of Piston. Looks Like Ring Was Torn Apart And Chewed Up In Cylinder Untill Heat Started Melting The Outside Edge Of Piston.

I had one in a 94 Baja 260 and had no problems at all. It was a new GM 454 HP 425 HP. I sold the boat and as far as I know it is still running.

electrical1,
Is the damage to your piston crown similar to the damage in this photo?

A budy of mine works for GM and they took a new car in for an engine problem and after checking it out found it was missing piston rings on one piston.

I just installed the same motor in my boat earlier this year a crate 454HO 425hp. No problems at all. Changed all accessories over and dropped it in. Smooth lots of tourque with no reversion problems.

Did I miss the answer or did you ever say which cylinder# it was on each engine? #7?

It can be tricky to get all the air pockets out of closed cooling systems when filled from empty. Best to fill the block through the removed tstat area. How was your cooling system primed? I ask this because you mention your water temp rising quickly as the first sign of trouble.

BT

Had a pair for 3 years now. No issues. Changed cams last year. Still good.

I believe it was #5 in both engines. In my opinion after talking with Electrical1 he purchased them from a non authorized dealer that will not warranty them and he is S**t out of luck. If there is anyone in Massachusetts that can help him out locally lets speak up. Would be awesome if someone had a spare engine to get Vinny going for the last few weeks we have remaining in our short lived season. We have all had "bad luck" seasons in the past and this truelly sucks!
On another note, its my opinion that when GM bored out this bank, one of the cutters had a defect. Evidently this is a bad batch of engines. Electrical1 needs to have the cylinder measured and compared to the rest for a fighting chance. If there is anyone that works directly for GM that can help him out by all means, speak up.