Pardon my intrusion, I'm not a V8 expert, but in that photo the head bolt looks very heavily coated with sludge while the valve springs etc and rocker area look pretty pristine, did you not replace the head bolts with a new set when rebuilding your engine? If not that could well be the reason for premi failure of the head gasket, many head bolts are TTY, (Torque To Yield), these days and will only cope with one time usage, they are pre-tensioned then tightened finally in two angle of rotation steps, to not replace all the bolts with new ones is a fatal error, not at all like the earlier engine head bolts/studs which were mostly re-usable and simply tightened with a torque wrench..