Pretty much everything cosmetic. It has the big flares including the little bits on the ends of the bumper. You can't put in the driver's side rear floor storage bucket as the chassis cab DEF tank is there, but since it sounds like you are describing a Dynamax I'm sure it's a regular cab anyway.
BTW - they make black 4500/5500 badges despite night editions never being a thing for those. I have the 4500 part numbers in the thread below, I didn't look up the 5500 numbers but they also exist.
Starting to get somewhere..
The backpack is taking shape. At this point the two uprights are welded to the bottom crossbar, but most of the rest is clamped together while I figured out the angles.
I am happy with the profile so far, although I did waste a solid hour today trying to figure out why things wouldn't center up. Turns out the cab is shifted 1/4" to one side. Yeah... Still deciding what to do about that, but odds are it'll just be what it will be as I'm not building the bed off center from the frame rails.
Next up will...
You can also get black 10 lug factory center caps if you are running them.