So I went to the Dealer ordering book for 1985, and found that the RPO TS6, High-mounted stop light, was listed as OPTIONAL equipment for 98 Regency, Calais, and Ciera LS and Ciera Brougham. Funny too, it shows a drawing of grid lines across the face of the brake light lens.
Which means Cutlass Supreme body styles would need to buy the high-stop mounted brake light accessory kit and have it dealer-installed if you wanted it. GM p/n 999375. Listed for less than 20 bucks back then. You can still find them on ebay here and there. Thing is, the universal kit is a tad different from year over year. The kit I had looked exactly like the factory unit but molded in black and had a factory style shield/rubber boot thing on it, but it was a tad longer with a steeper angle which would need to be cut to fit a G47 body style.
Which means Cutlass Supreme body styles would need to buy the high-stop mounted brake light accessory kit and have it dealer-installed if you wanted it. GM p/n 999375. Listed for less than 20 bucks back then. You can still find them on ebay here and there. Thing is, the universal kit is a tad different from year over year. The kit I had looked exactly like the factory unit but molded in black and had a factory style shield/rubber boot thing on it, but it was a tad longer with a steeper angle which would need to be cut to fit a G47 body style.