As said before you can't get 3.9 to work with 3.73.You won't even be able to drive it.... If you are having a hard time finding a matching different Assy. Consider a new gear set. In your thinking that a little is okay. ..wrong.On a 4x4 even as much as a 1/4" difference in tire size will destroy a frontend.matching tire brands and sizes are a must. If using mixing brands of tires one needs to measure surface circumference to make sure tires are as close as possible. I'm comfortable being with in 1/8". I say this because if mismatched tires create problems then mismatched gears etc create disasters. Yes some 4x4 setup have a slight ratio difference,as noted before,I'm not arguing that at all. I have repair many 4x4 vehicles that have had failures due to wrong gear set or mismatched tires.I cringe when I hear people who believe they can get away with being somewhat close..Close counts only in horseshoes and hand grenades. In mechanics you do it right or not at all.
