@firstgenaddict - The bolt is one piece. The threads are fine on the nut side and standard on the opposite.The washer is a flat washer.
@169INDY - The two bolts listed in the AIM for the pump are standard style bolts. A picture of a complete ready to install pump system is pictured on Jerry's website on the link below and you can see the two bolt heads.
http://z28camaro.com/rare-nos-parts/I have done 68 engine installations before. However, I have never mounted an air pump before. So I "assumed" it was part of that assembly when I first saw it. When I put together all my info, pics, AIM pages and so for the project I realized I had this extra bolt. I'm not a fan of leftover parts. I have searched and searched with no success so I posted the picture here.
@69Z8--RS - I'm with you about the familiarity and at the moment my brain remembers it as possibly a power steering bracket bolt on a 68 SS 396 Chevelle. A car I had 40 years ago.
In the end, I greatly appreciate the help. I am beginning to feel that it somehow just found its way into the mechanics box of sort trays.