It is not a Remington; it certainly looks like a Whitney Navy, converted, probably to .38 rimfire. The cylinder is not percussion and the rammer has been removed. It could be an original which was converted in the post-CW era. But my instinct on seeing a revolver like that with missing parts is to suspect a "kit gun" that someone got tired of when it turned out not to be easy to complete.
IIRC, Whitney copies, like others, were/are sold as kit guns and conversion cylinders/hammers have been available. Similar brass frame "Confederate" revolvers have also been sold.
What markings are present? If there are none, or if there are any indications that it is a repro (like Italian proof marks), the issue of age is settled.
Jim