Those aren't Colt style numbers, nor where they would be stamped. Are there any numbers on the bottom of frame, bbl lug, TG, or BS? Is there any bbl address? Looks kinda like a '49 pocket. My guess, A brevett.
I sure looks like a Griswold & Gunnison but the chances of finding a real G&G being sold as a near relic 1851 Navy for relic prices is infinitesimally small. With how weird that grip shape is it does not match any repro that I've ever seen so it's either the real deal or a good fake. Not real sure but I think a real G&G would have twisted iron barrel and cylinder and bronze, not brass, frame.
ok - received the mystery revolver in the mail. More photos.
The grip angle is ever so slightly swept back; when the butt is flat on the table the muzzle is raised by maybe a few (under 5 but definitely not parallel) degrees.
The barrel has what look like the striations of the twisted iron but nothing discernible on the cylinder. But it's so worn, pitted I can't really tell. The grip is obviously 2 piece and no markings on the wood inside or out. The main spring has also been replaced (and the screw) obviously at some point. There are stamps on the grip frame sides, a "R" and a "3." The underside has the 2 last SNs also. Nothing else on the loading lever or barrel underside. The barrel wedge looks like a simple cut bar steel replacement and its screw might be modern also but the rest of the screws seem period...whatever that period may be.
"Confederate Revolvers" (Bill Gary) and "Confederate Handguns" (William Albaugh) both show photos of G&G's with and without a cap groove. In fact, Albaugh shows a photo of #1037 and #1038 together, right side view. #1037 has no cap groove while #1038 has a cap groove. These were basically hand-made guns so there were probably other differences.
Is that a brass screw in the bottom of the frame/trigger guard? Is there a crack in it? And a crack in the backstrap ear? Old brass cracks. The screws look handmade. I would check the threads. The hammer and trigger guard are both weirdly shaped. I am no expert but if this is fake it's a really good one.
I have owned an original Griswold in the past, and this one looks quite legit. It has the characteristics, markings, and aging I would expect; and it's definitely not made from anything Italian. If it's a copy, it's time to get out of the hobby.