They will not be identical but they might fit. The DeVille had minor changes to the interior and exterior in 97. 94 through 96 will work for sure, and 97 through 01 fit each other, then 02 through about 06 are the same but completely different from 01 and earlier.
no, after '93 the interior style changed along with the door panels, they will fit on the door, but you will not be able to close the door unless you have the '94 and up dash
Pry bar and a hammer
No
94 and 01 are different models. my friend has a 98 which is the 94-98 model and his window control is different so it will not fit. the door handle is the same but overall the door cover or panel is different in style. i suggest going to your local junkyard and getting a 94-98 door panel. make sure the color is right though. EDIT: 94-04 Mustangs shared door panels alike. What you will need to transfer over is the "pocket" with the handle most people use to close the door, so that the buttons will fit. other than that it's the same. The color may be slightly mismatched in a black interior, but other than that, you should be in for smooth sailing.
I don't see why not. You'll probobly have to switch all the accessories for it too but The deville hasn't really changed very much since 1994 in fact in 94 it came with the option of the 4.9 and the 4.6 Northtar that comes standard in the 01.
No 94-2001 are a different body style and will not fit.
Yes
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YES.
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Yes
I am sure it will not. Call any salvage yard and they will tell you. I hope this helps you. Mark