Fortunately (... or unfortunately, I suppose, depending on your point of view ...) "in the spirit of firearms of the era" is not (and, to the best of my knowledge, never has been) a criterion for approval of a particular firearm in NCOWS, the entire philosophy of which is to stress historical authenticity.
The straight-forward relevant rule is: "Cartridge firearms shall be original to the period or authentic reproductions of original makes and models."
Now, I wish I had one of those lovely HRA Henry rifles (.... or even a Uberti-made one, for that matter ....) but my Uberti Model 1866 and 1873 rifles will have to do for now ....