Not sure if AM/FM/8 Track was an option in 73. This is my 73 radio with AM/8 Track, the plugs are different and the pushbuttons are in different locations.
8-tracks were only available with AM for 71-3's from what I remember.
Your probably came out of 1973 or later (til ??? year???) LTD, Galaxie, Country Squire, Torino, Ranchero.
Also see referrence to 74-78 Mustang II application.
possible pn D3AZ-18806-A
Ford Parts Dept sold as an accessory the floor or under-dash mounted 8-track player. It was more common to earlier(about 66-70) cars. The one I remember looked simialr to the pic but the outside case was covered in padded vinyl or a softer plastic.
It looks like the old 8 track out of my dads old 1970's ford truck
http://www.fordmuscleforums.com/TEX/8Track/2_8Track.jpg here is a picture i found of the same one as yours i think...Guy does not state what ford it come out of..But he was sticking it in a 1979 ranchero..could be a late 70's 8 track.
The funny thing is the wiring plugs right in like it was original. There are no splices in any of the wiring but my dealer invoice said the car came with an AM/FM radio.
FYI: note that the typeface on the frequency indicator matches many Ford products of the time, while the Matador's radio is styled to match the typeface of the AMC dash.
I thinking it a 1974 model. It a motorola I can read the tag. The nice thing is it still works. The 8 tracks works but I can't find any good tapes anywhere. There all 40 years old and end up breaking after a few plays. Old brittle tape.