I picked up a 70's ? Grayling green thats 60 inches long .I need a string .What length do I need? 57" possibly?
If you go by the actual string length, and you are using a non FF string, the 56". Some string makers measure their strings under 100# tension (that's the actual AMO standard), then 57" should be very close.
56" B-50 is what I would use and do use.
I like to go by actual string length. How you like it braced could make around an inch difference. If you don't have an existing string, I'd start with 56.5" (measured according to AMO specs like Alan noted), B-55, 12-14 strands.