Please see the ALR library listing for Joe Long. The Joe Long rifles at the bottom of the thread are typical products for this maker. The information I posted (and subsequently was moved to the library) is about all that we know at this point. Now on to the subject at hand--Amos Benfer.
Amos Benfer lived in Benfer and Troxelville, Snyder County, Pennsylvania. Benfer is very close to Joe Long's shop and thus, it is possible and plausible that Amos Benfer at least knew Joe Long. If Amos Benfer was born in 1861, Joe Long died when Benfer was 11 years old (1872). I think this eliminates the theory that Benfer apprenticed to Joe Long. I knew a relative of Benfer, who remembered him early in his life. Amos Benfer was not a full time gunmaker, but was instead a farmer, who dabbled with gun building. Most of the signed Amos Benfer rifles are relatively crude (being made of mostly mass produced parts), as compared to other Snyder County rifles. Benfer did, however, still have the roman nose stock profile of other Upper Susquehanna guns. That is not to say that Benfer was a "bad" maker, but he was building rifles after most had traded their black powder rifles for lever actions. There are a few early Benfer guns that do in fact look like other rifles from the region, but they are often unsigned, but attributed via family stories (if these are reliable). The known signed rifles are stamped "Amos Benfer [over] Troxelville, Pennsylvania."
It is great that you are a descendant of Amos Benfer and I certainly do not want to discourage you from building a Benfer rifle. Depending on what type of rifle you want to build, a Benfer style may not be what you ultimately want for hunting and shooting. It will look much like a mass produced gun, rather than what you may actually want to hunt with or shoot.