The '08 wheels will mount up to any HD Ram back to at least 1988, probably back to the 70s.
I have a set of take-off 2007 forged aluminum wheels and tires; they fit all the Dodge diesels.
3rd gen alloys have the same bolt pattern as the gen I but because they are 18's the will rub on the tie rod ends.
But all Gen III 2500/3500 are interchangeable.