Thank you for the response. My wife wants a radio with a cassette player. I can't find any for a 72 Mustang only for the 65-66 Mustang. I don't want to butcher the dash for an aftermarket radio/cassette player. I guess I'll keep looking at EBay and hopefully one will show up.
i have an aftermarket cassette player in my 64 falcon futura. because of an interior trim piece in the car it needs a different radio than the standard falcons use. i didnt cut the dash to use that radio. i would start by going to electronics sales and start measuring head units until you find one that fits the opening.
What does your dash hole look like? Retro Autosound has a lot of kits with adjustable knobs(horizontal and vertical axis) that will fit a ton of different vehicles...probably your best bet. The '66 radio:. 5 3/4" knob spacing(center to center) 3 7/8 x 2" faceplate opening, this picture will help with the knob centerline offset:
P.S. I would think twice about a cassette player....but then, cassettes and 8 tracks were always bad about being eaten by the decks...far better off to have a tape player that connects with the head unit via an aux input.