I have one of each and from what I can see,the differences are all cosmetic.The Fairmont has different door trims with bigger armrests,different seat pattern,extra interior lights in the rear pillars,plastic chrome interior door handle surrounds (I think),a boot light,chrome sill trims and wheel arch trims,a honeycomb panel across the rear,chrome trim on the top of the doors extending to the base of the rear pillar,a folding armrest in the rear seat,padded glove box lid, different hubcaps if not a GS,and a full length protection strip down the side.If either car is a GS it will have the GS dash,bonnet,steering wheel,12 slotters,and possibly a 4 headlight grille.The GS Falcon will also have a side stripe,but the GS Fairmont probably won't if it has the protection strip.I have probably left something out but I'm sure someone else will pick me up.