Jerry A,
I think experimenting with the timing is a very good first step. Detonation can surely blast a piston to pieces, but it seems you would have heard pinging and knocking long before it got serious enough to do this. The lean fuel/air mixture would only have adverse effects under the most extreme conditions and for a prolonged period of time. I'm certainly not a race engine mechanic, but I think something else might have been responsible for your piston failure, and I wouldn't be hesitant to fiddle with the timing all you want. The engine will tell you when it doesn't like what you have done...long before it will commit seppuku .
Stuart
