I "think" a 71 fender would fit (one w/o the gills) but due to the differences in the grilles there might be some issues in that area (which might be what you are seeing). 72-74 fenders would bolt up but the marker lights are completely different whereas I believe the 70 and 71 used the same marker lights.
Generally, there is a lot of adjustment in the fenders, your issue with the grille might be a result of the fender adjustment. The antenna hole can be worked with/around if necessary.
70 Challenger RT 440-6, 73 Cuda (under const)
05 Durango, 99 Dakota, 01 Ram 4x4, 14 2500 4X4, 10 PCP Challenger RT, 01 Viper GTS ACR, 52 B3B w/330 Desoto Hemi, 70 Hemi RR, 61 Jeep FC170
9 x Challengers. AAR Cuda, 4 RR, 2 GTX, 4 Chargers, etc... (too many to list)