Wow. This is painful.
Diablo: Kris is right. I was having all the same problems you mentioned. Ducting appears to be very important, mine seems to run cooler with a ducted cowl that without a cowl - go figure. Its very important to make sure the air runs over the tops of the cylinders and has a large exit - 3 to 1 inlet to exit isnt enough, it needs closer to 4 to 1. I started with no ducting, and overheated rapidly, then ducted about 1/4 inch above the bottom of the jugs and got good results but still a tad warm, moved the ducting up to 1/2 inch above the bottom of the jugs and that seems to be the right spot. Also, I tried an NX26x10, a MenzS26x10, a Mezjlik 26x10 and 26x10n, best pull came from the Mezjlik 26x10 turning about 6500rpm, the coolest run was with the 26x10n at 6800rpm, but it doesnt have quite the vertical, and rips very easily in the air and I have noise issues to contend with.