Thanks Steve. I know early Springfields reasonably well, and have grown more interested in mixed, pre-1795 assemblies, along with era state/militia muskets, but definitely not an expert. That said, I'm not finding any examples of 1728 plates with script lettering, or 1763/66 plates with block lettering, but could certainly be wrong.
That makes sense, re state armory. Didn't know if it was that, in the years after the war, or maybe mid-war sourcing/assembly, as state militias and continentals scrambled for arms.
Cheers