My '83 Bronco has a '95 4.9L, '78 NP435, 3.08, 32x11.50R15, and it does pretty well. I can tow anything with wheels (up to an 18-wheeler-sized dump truck) and a lot of things without (a house off its foundation, a construction office trailer, a 40hp tractor, a 30yd construction dumpster...), but I can also set the cruise over 100mph.
So I doubt you'll be happy with such low gears. The lowest I'd go would be 3.55, but for me, even that is too low. I could barely hit 90 when I used them. Yeah, the takeoff was GREAT, but the speed was pitiful.
Why are you so anxious to ditch the OD? Most people WANT it, although most try for the ZF (M5OD-HD) instead of the Mazda that you have. However, havack (BroncoData
) put one in his 5.0L Bronco and loved it.