I think the front speakers are 4 inch or 4.5 inch. They screw into the footwell, and protrude into the bonnet area where their back is covered by a black plastic cover. Without changing the rear cover you are very limited to what you can fit as they can't be very deep.
Exactly....they are 4" but anything with a cast metal chassis and a good magnet would need a new cover. Not impossible, but I agree with Alistair, replace the back ones first......
