Inspect the bow--check the riser and especially the edges of the limbs for cracks and/or separations. As long as the bow is in decent shape, you can string it. Use a bow stringer.

AMO is 3" shorter, longbow or recurve--but a lot of bows don't follow AMO specs. Most of the old Bearrecurves do get a string around 4" shorter. You won't hurt the bow using a 57" string, but a 56" will probably fit it better.

Chad