I've looked into this too because I don't "need" a dually. Anyway, I think I found out that the cab and chassis rear ends were more narror than regular pickup dually rear ends. I think the C&C will be 1" narrower per side than the front and I think that the regular Dually rear end will be 1" wider per side than the front.
Can anyone confirm this?
I've seen tucks that were converted using the regular dually axle and you really couldn't tell that the rear was wider unless you looked close.
I think you gotta change the bed, though. If you take the dual fenders off, the wheelwells will be all hacked up.
Jason