I have a 2007 MegaCab and, yes, it is on the 2500 frame and suspension. They de-rated the rear springs for the 1/2T designation.
I have not seen a lowering kit for the MegaCab but a good suspension shop might have some ideas. Not sure how many there are in Muscatine but it might be worth pursuing.
I went up 4" with mine despite the wife complaining about needing a ladder to get into it.