1960 F250. You might have the 4.56 gears. What is your axle code on the rating plate? No matter whar rear gears, and F100 or F250, the 4 speed transmission was the same (Warner T98A). Changing axle ratio will have no effect on transmission. What ratio to use depends on how you will use the truck. You have a low enough first gear to get an empty truck rolling with any sane axle ratio.