Early 97's generally. 97-99ish also used the upper bolt with a U-nut to secure the flange on top of the fender. After that, the hole and square hole to insert the U-nut is still there but the hole in the fender flange disappeared. Around 03 ish, there are tabs inside the grill for the temp senders for the compass mirror and air temp for something to do with the engine, one on each side. The early grills only have one.
A minor detail - the screw grommets that the headlight trim ring screws go into are different 97-02 and 03-06. The early grommets fit in a slot in the tabs and the later grommets fit in a square hole. The grommets are incompatible but the headlight trim rings are the same so as long as the grille you get has the grommets your trim rings will work with either but if you get a later grille that doesn't have the screw grommets you won't be able to use the grommets that are in your early grille.