Rear Axle Length
OK here we go
24-21.375 = 2.625
2.625/2 = 1.3125
1.3125 is the amount of your pinion offset. Now to get an imaginary line in the middle of the axle assembly, which will make it line up with the carrier center pin, you add 1.3125 to the short side and subtract that same amount from the long side...the number should be equal.
24-1.3125 = 22.6875
21.375 + 1.3125 = 22.6875
22.6875 * 2 = 45.375
45.375 + 5.05 (brake standoff/backing plate thickness) = 50.425 without drum thickness
50.425 - 1.75 air gap = 48.675 total axle lengths
48.675/2 = 24.3375 per axle if centered
Now you have to add/subtract the pinion offset because one tube is longer than the other.
24.3375 - .65625 = 23.68125
23.68125 + 1.3125 = 24.99375 or 24.3375 = .65625 = 24.99375
So the axles need to be 23.68125 and 24.99375
I have a whole write up in a word doc I'll post up.