I am running a 4.10 rear axle with the NV3500 overdrive (0.78 ratio) so I believe that equates to a 3.2 final ratio but I am also running a 383 SBC so I have a lot more engine torque available than those running a version of the in-line 6 cylinder engines.
Engine speed at 60 mph will vary depending on tire size in addition to overal drive ratio. I was trying to get taller tires to be closer to the original and lowest engine speed but settled for LT215/85R16's that seemed to be the best combination of diameter and width (narrow) for ease of turning (no power steering).
