If you can find the 4.11 gears that will help the Eaton axle go faster. Some people are still searching them though not alot available. You could put a 14 bolt or Dana 60 or 70 under them and get a much lower ratio gear set and still keep the 3/4 and 1 ton capacity. 14 bolts can sometimes be found cheaper than a Dana, but the new gear set won't be cheap for either.
I'm keeping the SM420 in mine, but gears is gears. If your gonna change the engine to a bent 8, then why not change the tranny as well (assuming it will all fit nicely). A 0.8 (or abouts) overdrive with a 3.38 gear set and some 285/70R/19.5 tires will give you a nice slow engine at 70 mph (1800 rpm). With this setup the question is do you have enough gear left in it to pull out stumps!
