calculate rear axle ratio

Wow! Never heard of doing it that way Walt and to be honest you totally lost me. Here's how you do it.

Jack both drive wheels off the ground. Put a mark on the driveshaft and one on a tire for reference.

If it's a sure grip rearend turn the wheels exactly one revolution and count how many times the driveshaft turns. If it turns slightly over 4 turns it's a 4:10 ratio. If it turns 3-1/2 times it's a 3.55 ratio, if it turns 2-3/4 times it's a 2.76 ratio, etc.

If it's not a sure grip, in other words it's an open differential, block one wheel from turning then turn the other exactly one revolution while counting the revolutions of the driveshaft. Multiply the revolutions of the driveshaft by 2 and that's your ratio. In other words if the driveshaft turns slightly over 2 turns it's a 4:10 ratio. If it turns 1-3/4 times it's a 3.55 ratio. If it turns 1-5/8 times it's a 3.23 ratio, etc.