OK, made the adjustment recommended and with two turns and both tires off the ground I got about 3.25 +/- full turns on the driveshaft.
With an open rear differential, it's possible that you'll be WAY off. The only way that would be correct is if you can be sure that both tires are turning the same amount of turns. If you turn both wheels 2 complete turns, you should get 6.14 turns of the driveshaft (assuming a 3.07 gear ratio.) A 3.07 gear ratio means that the driveshaft turns 3.07 times for ONE turn of the ring gear.
I'd recommend you use the push the truck for one turn of the rear wheels and then count the driveshaft turn, using the string method above.
At this point, it might be quicker to remove the rear axle cover and look for the stamping on the ring gear that will indicate the gear ratio.
