There are several small differences, but the easy one to spot at a glance is the raised bosses on each side of the reciever adjacent to the barrel on the G-2 where the original Contender has a completely flat sided reciever. Sorry to hear about your B-I-L, but he left you a great gun which ever it may be. Good Luck with it.
Walt
BTW If you'll look at the pictures in the adjacent thread titled "transformation" by hunt45-70 you'll see a G-2 in the top pic and an original Contender in the lower photo.