Steel Soldiers now has a few new forums, read more about it at: New Munitions Forums!
Microsoft MSN, Live, Hotmail, Outlook email users may not be receiving emails. We are working to resolve this issue. Please add support@steelsoldiers.com to your trusted contacts.
Did you look at the SNs over at g741.org in the registry? Lots to compare to.
Looks like that is a valid SN but it's listed as a build date in March 1959 and it does show the dashes in the places you listed.