Sounds like the rich LSN, wide idle gap thing to me.
Check your idle gap is really tiny (.7mm). Richen top end to flush with the barrel then start leaning the LSN until you get a steady idle and good results on the pinch test. Lastly, adjust your idle if necessary. The Go Tech motors are really touchy on the LSN. Once you get this right you will be sweet.
I had exactly the same problems. Plugs blowing all the time, running OK but running very hot at the end of a tank, piston and button very black. All caused by too wide an idle gap and a rich LSN giving a false "normal" idle.
Sounds lke you may have had a couple of small air leaks too, which wouldn't have been helping.