They're the same flare, 3500HD and 4X4. You can get look-alikes of them from LMC but I don't know if they are exact copies.
Sort of a PITA to adapt them to trucks that didn't come with the flares, as there are 6 large holes on the side of the fender, and studs hook into the flares so you can back them up with 10mm PAL nuts. Not only do the fenders need the holes on the outside but a few extra holes are on the inside so you can get in to do the nuts. Plus, fender has to be off the truck for you to do this because a couple of them are totally inaccessible with the fender installed.
Worth it though depending on your direction with the truck, they're necessary on 3500HD's because the tires stick out so much. They can also look good on a lowered truck like if you check BHB's reg cab dually that he added the flares to.
Richard