So, you have a hatchback with folding rear seats. And the Mustang convertible seats I assume do not??? If they do then use a tape measure and observe how the mount functions. Anything is a possibility. I once use the rear seats from a Datsun 2+2 280Z in the back of my Datsun 510. For the 6 months it was my daily driver the kiddies had to sit somewhere.