Tom shared pictures of this with me a couple years ago so I've had time to think about this rifle. I see a couple details found on rifles shown in Shumway's Rifles of Colonial America.
First is the sideplate which is identical to the sideplate on RCA 124, an early, walnut-stocked rifle that came out of Virginia. The guard is not dissimilar to the guard on RCA 124; also the guard on the Free Born rifle comes to mind for me.
Second is that the underside of the cheekpiece, in the way it tapers, is similar to the Brass Barreled Rifle (RCA 103) and the Germanic gun RCA 102.
Next, although it lacks a "step", the way the stock tapers to the buttplate is reminiscent of several early rifles or smooth rifles including RCA 102.
Last and perhaps least, the nose of the comb which I call "the dolphin" reminds me of the comb on RCA 120, a gun with English styling that may have come out of Johnstown NY.
To me the most telling features when we look for "kin" are the sideplate, which is of a rare form, the form of the cheekpiece, and the taper of the stock behind the cheekpiece to the buttplate. I think this rifle was probably stocked quickly and efficiently by a skilled hand, using mostly planes and spokeshave. Whether or not it is a restock or a "parts gun" assembled for the Revolutionary War using some parts from an earlier gun, is a question worthy of consideration. When I note the high quality lock and the rough and ready (but bold and skilled) stocking, my imagination leads me in that direction. The buttplate in its dimensions appears later in style (1770-1780) than the lock or stocking style. But in the early days I am sure there was a lot of recycling of parts, especially quality parts like that lock.
(I did some editing)