Do you have pictures? Where exactly is the scoring.? How much is "a little extra clearance" on the one rebuild? How much clearance did you give the Hypereutectic pistons?
.050" off the head and flat top pistons? How far past 10:1 are you? Joe H mentioned a week spot under front driver side head bolt. You can see it from the water pump cavity.
Someone -strike that. Everyone wants to know if a thermistat is being used. 3500 miles before the problem shows up. Ya, well, maybe, maybe not, maybe so.

eek cool A blue oval guy in bow tie country :p
Found another great bunch of guys the other day at lincolnsonline


'67 GMC 3/4 292 4spd