FYI, later M-Bodies like Diplomats used a plate that bolts right to an A-Body and has holes that match the minivan wiper motor. Seems like the motor is different, little fuzzy on that right now.
Either way, I have the Diplomat/minivan assembly that I have had bolted to my '74 in the past. Didn't hook up the linkage or wire it in though. My brother was going to use it on his Demon project and couldn't get the arm to work so it might not be a slam dunk.