8.75 measures 52 5/8 flange to flange

52 5/8 is correct.

That POS chart needs to be removed or corrected. More than a few have shortened a rear to that 51.40 size and been surprised!.

If you want correct measurements for 8.75 rears, bookmark this page:
http://www.moparts.org/Tech/Archive/axle/16.html