You were indeed correct. No BC on the bell, but a run-of-the-mill Evette-Schaeffer from the late 60's. The repair tech is new and read the serial number from the wrong book as you projected.
Looked like a solid horn for being stuck in an attic for 20+ years... but the guy paid $600 for it and it needed somewhere in that ballpark for a total repair job too. All in all, he just came and picked it up and went on his way.