Based on the markings, I suppose it could be either a 54” bow or a 58” bow. I assume you measured along the recurves and not directly nock-to-nock? If so you probably have a 54” bow, and your 49” string might work, although it seems a little short to me. If it is a dacron string, which it should be, it might stretch to fit after a little shooting. When you string it, the distance from the string to the inside of the handle should be about 7 - 7 1/2”, which is the brace height. Don't try to string it if it looks like the brace height will be 8 1/2” or more. You might be able to find out a more precise brace height for that bow from someone.