Anyone here ever have their pistons machined?

FD, maybe I missed the passages about your A/F ratio tuning, but while 13.0 WOT is typical, but not necessarily ideal for every engine.

Did you ever dip it down to the 12.5 or so range during all your tuning?
Did you try fattening up the mixture when you slowed the timing?
Did you ever try running a colder plug?

I know I should probably re-read the original thread, but hey, you're here now