'70 fenders have a vertical flange in the headlight bucket area, where the headlight bezel meets the centre grille.

You would need to cut these off in order to get clearance for the '71 grille. Plus use the '71 header panel as mentioned.


'72-4 fenders do not have the flange and it may be easier/cleaner to swap the earlier marker lights than to trim/reinforce the flange properly.