Depends on if you want an overdrive final gear, and yeh, they were some weaker. What Mopar (and others including Ford) did was to essentially turn the 3/4 shift lever upside down, so that the shifter treated the old 3rd gear in the gearbox as 4th gear, AKA the OD box shifted the actual gearbox 1-2-4-3 as you moved the lever 1-2-3-4
