The easy rear gear swaps from a 10 bolt 64-72 will give you 4.57 or 4.10 gears. All that's involved is swapping out the pumpkin (center section).
With a 700R4 tranny, overdrive is .70, which will give you final drive ratios of 3.60(5.14), 3.20(4.57), 2.87(4.10).
The 4.10 gears are getting harder to find, but are still out there. There are guys who have made the swap on 3/4 tons who would probably give you their old 4.57 gears.
