A few questions. How many miles were on the engine? Did you have any head work or block work done? Did the engine have the little tubes in the header that stick into the head for the PAIRS system? Was the PAIRS system removed but the little tubes stayed in? On torquing down the head, was it just one bolt that slipped? (Since you are tearing it down, I strongly recommend putting in studs!) Did you use high compression pistons, or have any other modifications from stock, like 're- indexed cams? A few answers to these questions can help identify the culprit. Thanks ,
John J.Cowall