The 4.57 gears were typical but 5.14 were an option in the 3/4-ton. You might want to confirm which you have because going with the 4.11 gears would be a big improvement over the 5.14s.
If you are running a 292 with a Powerglide another choice is worth looking at. The 700r4 or 4l60 overdrive automatics would bolt right up to the 292 and give you about 30% overdrive giving you 1.3 times 55 or about 72 as a cruising speed.
That 292 and Powerglide are not original in that truck. Are you sure that is what it has?
