M3 mirrors on E46 sedan or touring? This mod can be done easily with these mirror bases because the outside is compatible with the OEM M3 mirror and the inside is compatible with sedan/touring door. I don't say it is perfect and like OEM, but you don't have to cut the M3 mirror base and cut/drill your door.
The surface of this alu mirror base is not too smooth due to casting in sand mold, CNC machining afterwards is also difficult, so test fit and some additional surface grinding have to be done before paint.