Hammer,
I have seen 2 different sets of headers come back from nitro plate, They look great.
One thing I can tell you about coating or plating something is the smoother the finish prior to coating the better your final product will look.
I can remember my first blower I sent off to have anodized coated. It was a non polished blower case and a polished snout.
When I got the parts back I was happy with the snout, it looked fantastic, but the blower case, It LOOKED LIKE SH_T!!!!!!!!
As a matter of fact, I bet it looked like the tunnel ram mentioned above...
I called the coating company up and asked them why the blower case looked so bad and their response was If you would have had a better finish on the case it wouldn't look so shi_ty.
They let me know they perform that service to polish surfaces prior to coating for an additional charge. They assumed I knew what I wanted and the work order did not have any notation for polishing the case. So, I got what I paid for.
Since then any time I send anything to get coated, it is smooth as a baby's a$$.... A show polish will give you your best results when coating.