First of all, this is certainly not a reproduction. The workmanship may not appear to be very good to you, but remember that you are viewing a rifle that has been used and abused and somewhat neglected for 150 years or more.
I checked all of my books, including Sellers and "Gun Trade In America" by Jerry Noble and Tom Moore, which contains a great many that are not in Sellers, and did not find A E Shanks. I did find in Noble & Moore's book, a Thomas Shanks, in Shegoygan, Wisconsin, and a William Shanks, in Olean, New York. I subsequently did a search of census records, looking for gunsmiths named Shanks. I found a Jacob Shank listed as a gunsmith in Aurora, Dearborn County, Indiana, in the 1870 census. He is not found in any published book, including Jeff Jaeger's new book, Indiana Gunmakers . A E Shanks might have been related to one or more of these, who knows? There are lots of signed rifles still out there with names that are still unknown/unlocated, this not unusual. If we knew all of the answers about early gunmakers, this wouldn't be near as much fun.