So is it getting too hot from detonation Matt? I'm guessing John Gregory has seen enough to know if there is a correctable cooling issue.
Could you find some race gas and try running it on that, just to check
Otherwise, I hope the work to get it down to a nice reliable c/r is successful.
Oh, another thought - if it is detonation, could you twin plug it (I like using other peoples cheque-books).
Cam