With 99% certainty, I know who made this rifle. This is a John Parks, Jr. rifle made in Snyder County. I have to admit that the stock profile is pretty pronounced for the Upper Susquehanna school, but note the football sideplate, which is consistent with other products of the region, including those rifles built by Joe Long, the Spechts, Baum, Laudenslager, St. Clair and others. Of course, these makers do not always use the football side plate, but they built rifles with this feature frequently enough to almost elevate the football sideplate to a signature for this region.
Both John Parks, Sr. and Jr. worked near present day Selinsgrove, Snyder County, Pennsylvania. I do not know the exact location of their shop, but I have been told that they lived south of Selinsgrove. This is mere speculation as to their exact location, but most books, including Sellers (relying on earlier work completed by Ewing and Gabel), place the Parks family in the Selinsgrove area. Other sources (and I don't have the exact cite in front of me) indicate that Parks, Jr. moved west to Huntingdon and possibly to Ohio (and further west) later in his career, but you definitely have an Upper Susquehanna rifle, here, not a product of the Lehigh Valley.
Please contribute to my educated guess. I suspect that Mr. Getz will confirm my post. Thank you for sharing your family "mystery," which is now solved (at least for me).
Jeff Spotts