The lock ring for the New Departure DD is similar to the D, but different in two ways:
1: The center hole is smaller as there is no lock nut on the drive side.
2: There is no groove for the stop light switch contact ring to ride in.
Some D rings did not have the groove for the contact ring. I've seen DD's set up with D rings and they work, but the gap in the lock ring to the drive-side cone is noticeable when the difference is known.
I think where you'll run into trouble will be the switch plate: the reaction disc might interfere.