tomjanemc,
Apologies for the tardy response -- not sure how I missed this given my interest and appreciation of Dauphin County rifles and gunsmiths. One of the challenges with Dauphin County gunsmiths, as you noted, is the dearth of research and written information. That is complicated by the absence of strong, unique characteristics within this "school". That said, there are characteristics of your Stahl rifle that echo those of Martin Shell Jr., John Ford and Michael Poorman.
In addition to the information you noted, Gardner's Small Arms Makers has the following:
C Stahl - Riflemaker of Lancaster, Pa about 1810-17
Christian Stall - Harrisburg, Pa, before and after 1817 (Though this is listed as "Stall", German last names were frequently spelled differently, i.e., Martin Schell)
I would also encourage you to add this rifle to the Library, maybe adding a few closeups of the forearm. In addition to being a beautiful piece, it also adds to the public information on Dauphin County gunsmiths.
Bill