There might be a date code. Some Plomb / PTII pliers made in the former JP Danielson plant continued to bear them. To be honest, yours don't have a classic JPD shape, and I think PTII started using other vendors (e.g., Chanbellock) for some pliers. But AA has some Proto era water pumps with codes. Derust, scrub hard, and look for three digits.
Water pump pliers were issued to GMTKs, but they may have been issued to other kits as well.
I'd like to see the rationale on that. Not challenging you guys. I would just like to see how you arrived at that production era. The MFD was used by Plomb as early as the mid- to late-40s. The earliest Proto markings continued using it, granted, also with a Los Angeles marking, a handy tell. AA dates MFD USA, no LA, to a vague "ca. 1957+" after that, ostensibly because they have no way of differentiating late 50s MFD from 60s or 70s MFD. In fact, AA has an example of the same exact tool as
@mgmlvks, including the extra, martial "U.S." marking, and they date it to the amorphously vague "ca. 1957+". What is your reasoning for dating it to Vietnam?