06 Harley Davidson Exhaust Questions

[howardgr]

Just bought an 06 HD edition F250 w/49K, and I am new to diesels. After having the truck for a few days now, I am looking to add a a few light mods. Mainly exhaust and tuner, as all i want is better towing performance and MPG's. Have decided on an SCT with tunes, but I am having a problem with the exhaust. It looks like the exhaust may have already been modified, as I believe the downpipe appears to be 4" already. The truck still has the cat, muff, and HD edition tip. Was the Harley Edition exhauast different than others (XL, XLT, Lariat)? Seems weird to me, becuase I know the exhaust appears to be 4", but I have never heard of or seen a 4" cat. I thought all of the cats in these things were 3.5" Would a tech at a dealer be able to tell on a visual inspection if its stock or not? My only concern is that I know most dealers don't have a good deisel tech on hand.

Lastly, I live in the Charlotte, NC area. Does anyone on here that lives in this area have a local dealer they would suggest to work with on diesels (mod friendly, ability ,expertise).

Please advise and thanks for your help.