I really do appreciate the expert opinion on this forum and if needed I'll replace the lug nuts with the correct one's if need be.I would say that your lug nuts are aftermarket because they are 13/16" hex. Also, I do not believe that the factory installed chrome Z28 lug nuts were stamped with the thread size. Your 3/4" lug nut wrench may (or may not) be original for your car. Is there a "O", "U", or other letter forged on the lug head? Compare it to the 1973 Camaro lug nut wrench in my photo. If you do want a 13/16" lug nut wrench I will check my collection and see if I have one that is close to the same dimensions (18", 4", 21" diagonal) as the 1973 lug nut wrench in my photo. If interested, $10 plus shipping. I can provide photos with dimensions.
But other owners with original cars have stated they also have 13/16 lug nuts, so I'm in a tough spot here.