Use 6.5 inch speakers for the fronts. I recently replaced my front speakers and my car year is a 93. I think the 6.75 inch speakers would be too big, plus the magnet might be too thick as well. While you are at it, you might as well put some Dynamat on the door.
I'm surprised the powers that be haven't deemed it necessary to relocate this thread to the "Audio" section. Anyway, if you want to save some money, see if you can buy Ice and Water Shield by the foot from the hardware store. It's basically the same thing as dynamat but costs a lot less. I'd just put a small piece on the sheetmetal directly behind the speaker, it'll help to prevent standing waves from forming inside the door, causing poor speaker operation and vibrations. Maybe like a 12"x12" square.
I was looking at their site the other day. They don't carry shit anymore. Infinity is the only speaker line they've got that's worth a damn and some RF stuff as well, but all their shit is WAY overpriced. They've got to be charging MSRP. For what they want for an Infinity Component set I can get 2 sets of MB Quart components elsewhere! I've never bought from them and now I remember why. I'm surprised they're still in business with prices like that. Must be a lot of people out there that don't shop around for stuff. www.ikesound.com has the best pricing I've seen and they carry some good brands.
I agree that Crutchfield is waaaaay overpriced, the only thing i will say, is that their customer service is great.
And Ike Sound has some great deals, i talked to a local shop where i know the owner, and some of the speakers from Ike Sound they are selling below what cost would be. Only problem with Ike Sound, is a somewhat limited selection as far as models and stuff.
My old car was a 1994 E model. It came with no speakers. The opening is pretty big, but the rail for the window is right behind it. You will have to make a spacer out of wood. You might have to cut as well. The other problem is that the grille on the door speaker was designed for a smaller speaker. So if you go with a bigger driver, you will have to cut some of the doorpanel out (shine a flashlight into your door speaker grilles and look at how much of the opening is blocked off).