As originally manufactured from the Remington factory, I have never seen anything other than the standard-length barrels on original New Model Army's & New Model Navy's.
I have seen many different barrel lengths when modified by frontier gunsmiths, and different barrel lengths on cartridge conversions (factory and non-factory).
While not technically historically correct, I still love my Pietta 5 1/2" Remington a lot!
Just my 2 cents,
John