It is good to find you again, and I see that you are still researching Navy flight gear used during the Vietnam War, which I continue to do so as well.
We were in regular contact last during 2008, until I moved to a different job in Texas (going back to my old lab, where we conduct forensic analysis of flight gear artifacts that are recovered from loss sites in South East Asia, involving US MIA personnel from the Vietnam War.
My new email is 'email@example.com, if you want to contact me, and discuss flight gear.
I will offer some good info about the Navy's black-colored Safety Boots used during VN.
This Military Specification is dated in June 1970, and the overall boot color was changed from Brown to Black. However, the overall boot design did not change, so this 1970 version boot is identical in design to it predecessors, aside from its black overall color (black leather uppers and outsoles).
Your Navy black boot picture appears to be a later (post-Vietnam) version black boot, which was different in using a modified chevron outsole, and smaller eyelets.
I include a photo of my late war vintage black Navy Safety Boots, which are dated October 1972, and thus, fall under the above June 1970 Mil Spec. My 1972 boots use the correct wartime rubber 'traction tread' outsole, which was the outsole type used after the earlier crepe' rubber outsole, and the Vibram type mountain rubber outsole.
Hope this info helps, and hope to hear from you soon.