Okay heres the thing, if you do it purely with skinning you can make an alpha channel on the skin so that it would appear as one head.
BUT the head will not be centered as the model has two heads that are off-centered.
If you would like to have it as one model, you will need to edit the model by removing either of the heads and then centering it.
This is very easy but its a filesize killer, unless its not a bnet game. So which way do you want to go with? I can do either way. Want me to edit the skin, or want me to edit the model as well as changing the skin path so that itd be one-headed with the proper skin.