The 60" is the AMO bow length. AMO string length will be 57", but you might prefer 56" or so, depending on what the bow likes. A 10 or 12 strand dacron (B-500 or B-500) string will work well on that one. If you have a string for it, get the brace set and measure that string to have a better idea of what you need.

Sounds like the serving is about to go on the Black Bear's string. You don't want the nock set slipping for sure. If it's in good shape otherwise, you can just get that string re-served. 12-14 strands of dacron should work fine on that one.

Chad