In my experience, jetting a 300 "super rich" isn't the answer; they are extremely sensitive to compression ratio. It sounds to me like the compression ratio was already incorrect with the LG inserts, and the race fuel (at some point) only just saved you from piston failure.

Fitting the UL inserts (even if they were correctly machined) has just shown up the compression ratio problem previously masked by the race fuel, and the lower octane/lead free fuel was unable to compensate for the incorrect setup any longer.

I would personally be inclined to pull both barrels and measure them.
_________________
Andy.
NSR-WORLD.COM

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