My H. Holland 360 double barrels are marked " Henry's Patent A&T 1887 [right barrel ] and 1888 [left ]. It was made mid 1875 . With your barrels being approx. 200 units later, my bet is that your rifle was made late 1875 to early 1876. I'm pretty sure the Patent Use number ran consecutively, no matter who made the rifle, Alex. Henry included. Also, it looks from the pics that the forend is secured by a wedge, another pointer to an early one.