Does anyone know what kind of susp. upgrades will work on a 79 DeVille? I heard that imp SS peices work on the coupe devilles.

Back in those years, most full-size GM cars shared a high degree of their suspension parts. This also included Cadillacs. The Fleetwood shared with only the commercial chassis and "some" police package parts, while the Deville (both coupe and sedan) shared with the full-size Chevy's, Olds, Buick's, and Pontiac's.