The Dodge MH Service manuals indicate that 73-74 RM400 used Bendix Twinplex rear brakes
and 74 later model M500 used Bendix Duo-Servo rear brakes however, none of the Dodge MH Parts manuals show
parts for 74 later model M500 Bendix Duo-Servo 15" x 4" configuration.
Additionaly, aftermarket parts sites only show parts for the Bendix Twinplex 15" x 4" rear brakes.
Given that I can only locate information for the Bendix Twinplex
15" x 4" rear brake configuration I only list parts for that configuration.