When I bought this poor sword/ bayonet I never even thought this could be the original blade. Thanks to all for the insight and the knowledge, I have learned a lot with this purchase and this forum.
It may well be the original blade. The US bayonets do not seem as curved as the European 'saber' (Yataghan) bayonets. All it takes is a good source of heat and a hammer. It certainly is NOT British - we were not into solid brass handles. It isn't a Sharps Bayonet the pommel is not curved enough. It isn't a Chassepot bayonet or the Colt revolving rifle as both slots run the length of the handle and the M1855 for the Mississippi rifle is also much longer. The slot is too long for the original M1841, M1859 or USN Merrill bayonets but seems right for the Remington Zouave bayonet.
There are so many variations, apparently, it is hard to pin down.