RE: vintage bear recurve
For a recurve, a string length that is 4" shorter than the ATA is a good place to start. Most will experiment with different brace heights to see where the bow shoots best and quietest. If you use modern string material, make sure the bow tips can handle it. Othewise, you have to go with dacron, which will continually creep, causing you to fiddle with twisting it on a continual basis.
I usually like to start around an 8" brace height and experiment from there.