[Jim McDougall]

It is unfortunate that there have been no replies to this query, but it is a difficult one to offer information on. I think you have done most reasonable research and thank you for sharing your findings.

What I can say in hopes of augmenting your position this far, is that the badly degenerated cartouche on the blade might be from a number of possible makers as you have acknowledged. These names in the borders of oval cartouches were a convention known to have been used by bladesmiths in the Milan, Brescian regions of Italy in these times, the Picinino group beng the most familiar.
Norman, as you have noted, describes some of the makers with connections to this type marking, and again, as you note, the type #58 hilt is the closest to your form. These are of course general forms, and certain peculiarities arose with varied makers . The period in early 17th century seems correct.

To compound the dilemma of classifying to a certain maker, the oval cartouche idea was used (as noted) by a number of makers in these regions and times, also German makers in their fashion spuriously used names etc.

I think your rapier is as noted early 17th century and the blade probably indeed from a maker in these Italian regions, but exact attribution further difficult if not unlikely.