just adding to above responses, even if you wish to fitter 'better' after market speakers you would be best to use the plastic housing of the original speakers as they are a really strange shape.
The front and rear are all the same speaker, so you can easily pick a pair up from a breaker, also the tweeters are all the same. I bought a set from A2steve a couple of years ago, two speakers and two tweeters plus he also supplied the connectors and a chunk of wiring harness. This allowed me to make up looms and the speaker install was all done in a couple of hours. If you are going to do it properly you will need to install pins and sockets in the door / B post plug and socket for the extra two wires (the connectors have spaces for these pin and sockets, or you can cheat and feed the wire through the little space below the socket and directly into the B pillar. This will prove problematic in the future if you ever need to remove a door !!!
I was using an aftermarket head unit therefore did not need the power amp under the drivers feet, as the head unit powered the rear and front speakers directly
Cheers,