Retro doesn’t include the Cutlass Supreme (mine is ‘91) in its compatibility list, but the bottom mounting bracket from the original unit fits on the bottom of this, needs to have couple of small protrusions cut/banged flat (3 minutes of bother), and then goes in effortlessly. Two small bolts, included, notch into the two square holes in the bottom of the faceplate. Only complaint: default connection cable is not compatible. Had to splice bare wire connectors (included) into the car’s harness before connecting to the final default connector. Also, four tiny bolts for mounting the faceplate to the motor are practically invisible in an almost opaque amber sachet inside another bag of random, mostly unnecessary, bits of hardware. They’re for the obligatory step one of assembly and should have prominently flagged, not buried among the just-in-case stuff. Now installed, great sound, great reception of distant stations the original had no hope of catching, and perfect classic match with the car. Kudos.