the only way that 20-50 would destroy an engine would be with a plugged by pass valve, a high volume pump, a sorry oil filter, and 100 psi oil pressure at start up. Then one would expect a collapsed oil filter element and no oil pressure.
Otherwise, on a new engine, one can suspect poor machine work, a bad engine assembly, or an owner that went into boost with no scan tool to show timing retard and detonation, or one that did not understand what the scan tool was telling him.
No way can you blame it on 20-50 oil. And, a properly built engine should never require heavier than 10-30 unless it was a race engine built with chevrolet clearances
20 psi of oil pressure on a new engine with 20-50 oil is awfully low for a properly built engine. Sounds like the problem was already there. I'll stick with the three causes in the second paragraph
