I just measured a standard small bolt axle from an A body rearend and it measures 25 7/8" from the back of the flange to the tip of the splines.
Also, your measurment of the perch location and flange length is critical in identifying the exact housing you have, so shoot us an exact measurment of the perches. A body rear end flange to flange is 51 5/8" and the perch center is 43". Good luck with your project, Geof