I would not cut the mounting tabs, the speaker should have all 4 screws in it to prevent vibration. Plus the tabs on your new speaker will not be as strong as the two on the factory. Also the new ones are 5 1/4'' which are smaller than factory, those two holes won't line up anyway. When I was installing, I would make adapters for mounting. Some times the speaker would sit in a recessed, odd shaped part of the door, so I would use the factory speaker as a template to get the overall shape then cut the center for the new one. Generaly I would use 1/4'' material for the adapter, sometimes thicker if I needed clearance for the window and had the room between the door panel. Some flat black paint before installation makes them almost disappear when finished.