when me and percy fitted my door speakers we took off the old speakers (13's) then using mole grips or strong scissors we cut the plastic of the speaker away leaving just the top plastic rim (with the perfect fit screw holes) we then attached the new speakers (I have Pioneer dual mag 13's) to the rim using 4 little screws in the new speaker holes direct to the rim. you can then attach that to the door, using the original rim of the speaker saves £15 you'd have to pay for an aftermarket adaptor or drilling into the door.
it may sound confusing but when you take the old speaker out just look at the thick plastic rim bit where the attachments are. keeping that bit intact just rip the rest of the speaker from this rim and hey presto you now have a ford adaptor piece for free. As Percy told me the market value on the old speakers is non-existent so you may aswell use what you can before you throw them away. and as a plus just ripping the plastic really gets rid of any aggression or stress
