From what I've heard, the gas-derived blocks were bulletproof and the bottom ends were fine; the biggest problems were the ridiculously lax head/ block deck specs, cheap head bolts, chain-driven Roosamasta and lack of a fuel-water separator.
The engineers that did the math to make the engine stand up to the higher pressures did a splendid job; it was the gas-engine mentality about the little things that killed the engine.
I would rather have an Olds than a 6.5 liter. With the head installed correctly they're supposed to be good little engines. :lol4: