I don't know how the Cuda filler is mounted but the Challenger fillers mount to the header panel and the grill. They don't mount to the bumper. Hold the filler up to the grill and see if it lines up. I don't see any holes in your grill but it's possible the holes were filled...or a grill from a 72 was used.
The bumper mounting holes are slotted. Right now the bumper could be pushed all the way forward. It may be as simple as pushing the bumper back farther.
Lightly sanding the filler with some fine wet/dry sandpaper will clean it up nicely. If it still looks old and dirty, it may need a little paint to look new again. I got lucky with my Challenger fillers...they look brand new after a light sanding.