So were all the bolts used on the intake manifold the same head marking? I removed some recently that have no marking at all. Then they would not be original I assume? The motor had minimal work done to it before my ownership, so I would not have thought these to be replaced? Hex head and Had washers underneath as well. Guess the washers prevent damage to the aluminum of the manifold.
Jimmy one other thing on the manifold bolts....my understanding is that (and it may be wrong) the manifold bolts were first installed at the engine plant and they were all the short ones. When the engine arrived at the auto assembly plant dress line, the short bolts were removed and the other ones added as the equipment was installed. Thus, you could have different head stampings because you are dealing with two different plants.
Oops, forgot something, the AIM states that the orange alternator bracket on the '68 Z28 was part of the engine assembly (wouldn't apply to a '69), so this item might get a longer bolt at the engine plant. Also the AIM states that the spark plug wire towers were also part of the engine assembly, but these were thinner so maybe they used the short bolts. I haven't been able to determine where the engine hooks were installed, at the engine plant or the assembly line dress plant. Maybe someone else might know for sure.