This is a left rear tail light bumper filler , includes left unit only as pictured.
Cadillacs Fleetwood, Brougham, Coupe, Deville from 1974, 1975, 1976
Made out of 3 layers of handlaid fiberglass, better quality then those ABS plastic injected units that break into several pieces at impact, fiberglass is repairable ABS much harder if at all repairable.