I thought I should mention that there is a difference in bolt head makers markings,bolt thread (fine /course), and nut style between the 67/68 years. I will let others organize the differences if they care to .
I would agree there are different bolt head markings and as seen in the O.P.'s image (O P claims original to his mid-December built San Jose example),
there looks to be two types found on a single 67 example, one type with an "A" centered on the bolt head and another with "R S C" around the 3 hardness marks (reposting OP's image here again for reference)
I am going over my tie rods and original hardware but I have mixed 3 full sets into my batches. (Using all 3 sets as a source of "best originals" to choose from). One set after cleaning in EvapoRust & tumbling are obviously not re-usable because of pitting, these can all be identified as NOT being from my car. The problem I have found is that I do not have a full 4 bolts in good condition in either the "A" marked bolts NOR the "R S C" marked bolts and now seeing the OP's bolts, I have to wonder if I had a mixed set also.
IS THIS POSSIBLE? (I would have thought all four bolts should be the same, but perhaps this is not true?)