Well, you never say never, but I don't see this being a Joe Long. The butt stock is pretty wide and "beefy," a lot less refined than most of Long's rifles. It has much more of a Milton shape.
The football sideplate is almost a universal feature of all Longs and it is lacking, here. Morrison and Filman also used the football sideplate, hence my "guess" of Morrison, as, again, this is lacking definitive Morrison characteristics (or at least what I have encountered).
Long rarely engraved his inlays and the engraving on the sideplate would be highly uncharteristic of his work. Long did have a tendency to put a small mark, representing the eye of the fish on fish inlays he often used. Any engarving that he used is a light squiqqle (chisel walk) around the inlays, but as stated, most Longs are not engraved and the particular engraving on this rifle would not fit with Long.