That is something. Per the knowledge base, that hull number does not correspond with it being a 1958, but I don't think the age really matters when it is that old. It is in great shape! http://kb.sunfishforum.com/images/history/timeline.pdf
BB, I could be wrong but I don't think the knowledge base timeline lists serial numbers for Sailfishes so it quite possible that it's a 1958. The fact that it's only had one owner probably means that they have all the documentation as well... Not that it really matters...