Or at least count driveshaft rotations per wheel rotation. It won't be as accurate, but would be close, less trouble and cleaner. I'd only worry and explore more deeply if the front count didn't match the rear. It will give you a pretty good idea of what the ratio is. I doubt someone would go to the trouble of changing a 3:54 to a 3:71. I bet it would be more drastic than that.
The tag only tells you how it was built at the factory. Once it leaves... who knows? ESPECIALLY on a 30 some odd year old Jeep.
I'd rather be lost on the trails than found at home!
If the front and rear ratios were that far different, you would notice right away. At one time I bought a CJ5 and later discovered it had mismatched ratios front and rear. The first time I used 4wd was on ice waiting in line with cars to go up to Lake Tahoe on Hwy 50. I applied the throttle to move forward, and there was no forward movement at all,-- as soon as the wheels started turning at different speeds, the Jeep immediately slid sidewise off the side of the road. I did the remainder of the trip in 2wd.
Thanks for the responses. I am probably going to open up both pumpkins anyway to make sure which I have, since I am going to re-power this thing hopefully soon. It's obvious that one of them changed, and I want to make sure I know what ratio I have. Since I am doing the pinion seal anyway, this is the perfect time.