Head Bolt, Stud Torque Tech Tip - Importance of a proper washer - Interesting

Hard to say for sure without knowing what was actually used. I would wonder if a washer was NOT used and the area got ground down. Or, if those upper bolt seats are not surrounded by metal at the same level, then the AL would seem to be subject to distortion and 'flowing' out. (AL has about half the shear strength of cast iron.) And the Edelbrock heads' upper seats are like that... isolated towers; IDK on others.

Any washer under the bolt head needs to be thick like an ARP washer, not thin. A thin washer will just bend and distort, and not be effective in spreading the loading around. So maybe you need wider thick washers than your kit....