I've been going through this for the last few weeks, doing research and e-mailing different guys from this list that have done this. I finally had to remove the door panel to fully understand what it looked like, and measure carefully what will fit or not. I found that there is a metal rail that the window slides up and down in, (the window glass slides inside a groove so if your speaker touched the metal rail the glass will still open and close) and measured carefully to find that there is about 3 1/4" max. of depth from that metal rail to the end of the dash with the door closed. Most of the slim fit 5 1/4" speakers are 1 3/4" mounting depth, so these would be the easist to fit, but several people are fitting a 6 1/2" speaker but these will take more custom trimming and building spacers to fit.
Spacers can be made from 1/4" tempered hardboard (the stuff that looks like pegboard but with out holes, and it's smooth on both sides) or even 1/2" MDF. I plan to make a spacer that fit's onto the metal where the original speaker mounted, and glue and screw it to the metal. Next I will remove the original grill covers from the door panel, then remount the door panel. Now depending on how deep your speaker is, you will check it's fit, and if it fits tightly in place your ready to drill and screw it to the door (wire the speaker first) If your speaker is still not sitting flush with the door panel you need to make another spacer that will fit on top of the door panel , so cut another spacer of the required thickness and check fit again. When it fits, you will want to shape the wood nicely and cover with a vinyl color of your choice and mount the speaker for a clean nice looking installation.
As far as speakers go, I kept going up in prices the more I listened to different ones and found which ones I liked the best then went to the NET and found I could save $100 by ordering them myself. I liked FOCAL speakers, and just ordered the 6 1/2" 165CA. Be advised that the 5 1/4" 130CA would be easier to fit, and the ones I ordered might not fit. If not I'll put them into the back doors or into my car. There are a lot of speakers made for shallower mounting depth, but nothing like the factory speaker. Eclipse, Infinity, JBL, Kenwood, Pioneer, to name a few. I decided that mounting them myself and saving a lot on the speakers is easily within most that are mechanically minded. Very few tools are required, a jigsaw and drill and screwdrivers.
I'll try to post some pictures of mine when finished
Hope this helps.
Bryan