I ne copy need a duplicate copy of my high school diploma. I graduated In 1977 from Largo HIgh School.

Have you tried calling Largo High school about it yet?

Best idea is to contact the high school. Why do you need a copy of the diploma? A copy of the diploma is not needed to go to college, or get a job. It's more for display, for nostalgia.

Also considering they are roughly 57-58 years old now...

Contact the school district you attended back then. You will likely have to pay for it however.