Chances are the gears are 3.73 or 3.54 .That is what most late model deisels carried.
Crack open the diff cover and check out what ratio they are.There will be a few numbers stamped into the ring gear.After the manufacturing dates there will be two sets of numbers like 41-11 .Devide one into the other and that is what the ratio is
I once heard that all diesel Scouts used 3.73 rear ends. I know that's what my Scout II has. Given the power of the engine (or lack thereof), I'm not sure it could move a truck with 3.54 gears. Good luck!