If your rig ia a 74 like your name, you should have 4.11's...Jack up one side of the rear, and spin. Watch the driveshaft. 4.11's will spin the drive shaft 4+ a little times, and 3.73's will spin it 3 and 3/4 times...this assumes no locker...if your locked, take both rear tires off the ground...
Actualy if you only lift one wheel fith an open diff you will have to make two revolutions of that tire to get one revolution of the ring gear. therefore two turns of the wheel will give you 4.11 or 3.7 turns of the D-shaft.
