An M-body is any:
1977-1989 Dodge Diplomat
1977-1981 Chrysler LeBaron
1977-1989 Plymouth Caravelle (Only in Canada)
1982-1989 Plymouth Gran Fury
1982 Chrysler New Yorker
1983-1989 Chrysler 5th Avenue
M-Bodies were offered as 2-door coupes, 4-door sedans, and 4-door station wagons from 1977-1981. From 1982 on only a 4-door sedan was offered. The 1981 LeBaron was offered as a police package and the Diplomat and Gran Fury/Caravelle were offered as police packages from 1981-1989.