FAB,
You didn't mention proof marks. If there are no proof marks and no importer marks, the barrel was possibly custom made, in the USA. If custom made, it would have been built to the owners wishes. The WW77 might be the gunsmith's initials and the date. At least after 68, a gunsmith was supposed to mark the caliber and identify the installer. I have no idea who WW would be, maybe someone else does.
Mike