For OE Wheels for the Gen 2, you have
17", 18" or 20" x 7.5" wide, ~6" backspace, 6x5.5 bolt pattern, 14mmx1.5 lugs, 3.06" center bore
18" or 20" x 8" wide, ~5.5" backspace, 6x5.5 bolt pattern, 12mmx1.25 lugs, 3.06" center bore
Some of the Gen 2 wheels use a flat seat lug nut and some use a conical seat.
The Gen 1 uses 6x5.5 bolt pattern, 12mmx1.25 lugs, 3.06" center bore. and came with either 5" or 5.5" backspace
So, yes Gen 2 wheel will fit, if they are from an XD, they are going to tuck under the fenders a lot more and wider tires could rub the suspension, also the holes for the lug nuts may be a little large and you may need to go buy lug nuts to fit them. If they are from the non-XD, You may need new lug nuts, the ones that came with the Gen 2 truck would work, or buy some aftermarket. The ones you have now may work.