Don't give up, KC...
The numbers/code do make identifying much easier if the donor bike isn't known. That's one reason why it is a good idea when getting rims re-chromed to ask the plater to preserve the stamps as best as possible. In my experience it can almost always be done (with varying degrees of success).
Gordon, I assume you know that in Bacon's BSA Singles Restoration bible, there are some index pages of wheel information for the various models, including rim stamps, sizes, etc... But no help here unfortunately.