We can try to help better with pictures BUT BCM should be black with white bellies and wing tips. Golden Cuckoos will ALL have spots. They are AUTOSEXING. The roos are much lighter in color like a milk choc brown color and the pullets should be darker. Someone posted a link above so you can look at what golden cuckoos should look like. Keep in mind not everyone selling Marans has good Marans.
Thanks for the help. Most of the BCM look exactly like what you're describing. None of the brown chicks have spots on their heads, so I'm not really sure. (I posted a picture on the previous page) I guess I'll know when their grown-up feathers come in. The guy I got the eggs from had beautiful birds and eggs, but then again, I'm new to this breed.