What rear other seats will fit a 63 falcon?
The 63 falcon uses the same seat as the 60/61/62 Falcon. A 65 or 65 seat would probably also fit but have never tried it myself. A 4 door or 2 door does not matter. convertibles are different though. The upholstery will be different between models but I assume you don't care about that. As far as what newer model cars would fit? Hard to say, best be would be to measures your opening, and go to a junk yard and start measuring. I have seen the seats (front and back) form an Oldsmobile Alero in a 64, The owner said they fit right in. But that's second hand so take it with a grain of salt.
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