Shaft Length

Answer per DrDiff-

This is when using OEM Mopar brakes 5x4.5 bolt pattern drums in the rear, with A body 8.75 axle housing and cone style (Borg Werner) sure grip

Axle overall length from edge of spline to outer flange of axle shaft = 28.0 in
Axle length from edge of splines to outer bearing journal of the axle = 25.5in

This will allow you to run the axles without taking the thrust block out of the sure grip and will give you maximum of 1/2in of spline engagement.

You can add 1/8in or cut at 25.625in from edge of splines on shaft to journal and also take out the thrust block to get maximum of .625in of spline engagement from axle shaft to sure grip.
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* This is also for OEM stock A body rear end with Mopar rear drums, and Mopar power lock sure grip.

For clutch type (power lock) sure grips axles are cut to 25.5 outside edge of splines to journal giving you overall length of 28in. BUT you have to take out the thrust buttons/block to get engagement of the shafts into the sure grip unit.