Definitely omi-no-yari, definitely a composite piece. The re-hilting feels honest, it was done by someone who knew how to make a sword; it would be in better shape but it looks like late in life somebody attacked an iron fence with it.
Since the blade was originally Nihonto, I don’t have to respect the patina, right?

The steel looks koto (pre-1600s), so once I’ve taken all the ripples out the rust is going away, and we’ll see what else the metal has to say about its origins.