Robbie,
You can't take anything for granted as many things may have been changed in these trucks since they were new. Try this method: Jack up one wheel, make a chalk mark on the driveshaft by the rear u-joint make another mark on the tire. Make 2 complete revolutions with the tire and count the number of revolutions the drive shaft made.
3 1/2 turns = approx 3:55 ratio, almost 4 probably 3:90's, a little over 4, probably 4:11's.
It's not exact but close. Of course it would be a good idea to look at the condition of the gears in the one you are getting, then you could count the teeth and be sure.
Fred
