Marc, I searched my records and the earliest Henry record I have is a page that starts with rifle 3668 a 450 double express rifle, 28" damascus barrels finished (maybe sold) on August 1875. It was made for a H A Fowler Esq.
Thanks for the compliment on the rifles. My brother and I started collecting double rifles in 1971, my first an 8 Bore W W Greener top lever double rifle I paid $750.00 for. We could never afford more than 2 or three at a time and kept buying and selling them till we upgraded our collection. Believe it or not, we went through over 120 double rifles, almost all black powder. The finest I ever owned (sold it too,dang it) was a cased Alex Henry .360 double rifle made for a landowner in Australia and had all of its reloading tools in oak and leather case in about 90% condition. Did I make some stupid decisions, you bet, but it was fun. Enjoy your Henry. I would call Dickson's and ask for John, he is very helpful with the records. Back when I started collecting, I saw a table at the Ohio Gun Collectors show that had a large row of black powder English double rifles at $400 to $600 each! If only I could have afforded to keep all of the ones I owned, but at least I had them for a while.