A minor amount of clarification. Technically, it's THIRD gear that's the OD. Both Ford and Mopar did a "trick" when they came out with the 4 speed OD boxes
Ma just flipped the 3-4 shift lever upside down, so when you move the SHIFTER 1-2-3-4 you are actually shifting the GEARBOX 1-2-4-3. Ma re-geared 3rd gear as an OD ration, and the "old" 4th gear now becomes your "new" 3rd gear.