79-82 Mustangs only had a driver's and rearview mirror as well as 0 cup holders. Ford completely re-designed the interior in 1987 to add ANOTHER ash tray and a FOLDING ARMREST but nooooo cup holders
in the 80's and 90's. But I have managed to modify a Chevy cup holder and put it in place of the useless ash tray with a missing door.
And those buttons? BUTT WARMERS!
(Yes its a mess, I am still working on it.)