Just from the head shot, I would assume that he is a barred rock. A simple way to tell them from the Cuckoos is the color of their legs. Barred Rocks are to have yellow legs(shanks) where the marans will have white legs/shanks.
Barred Rock
Cuckoo Maran
If you will look closely at the barring on the feathers, you will notice the diffence in the barring. The Barred Rock's bars are thinner, and more uniform. Where the Cuckoo marans are thicker and more splotchey. I hope this helps.
oh kool, cuz we had no idea what it was, this old guy hatched him out last year but the old man died a few days ago an his daughter gave my uncle the rooster