Yep, that could indeed be a Henry. It has a long barrel and as we all know there were no short barreled Henry's. However it seems like I can see case hardening on the receiver, if that's the case then it is a 73 rifle. The pistol in the belt of the fellow in the middle looks like a Starr DA and the gent on the left holds some kind of a cut down CW type musket. Looks like Kelly's coat is buckskin with short fringe, similar to the one that Custer wore. The collar is off center and it does look like fur, but he is wearing a neckerchief that blurrs his neckline. Looks like he is wearing tall moccasins, but they don't date anything.
I'd date the picture "ca. 1868" and be within a year or so, since I tend to think that is a Henry.