B body 8 3/4

All 8 3/4 rear ends. Info from: http://www.moparts.org/Tech/Archive/axle/17.html

66-72 A-body rear end is 57 1/8" drum to drum

65-67 B-body rear end is 59 1/2" drum to drum... 2 3/8" wider than A-body... 1 3/16" wider on each side

68-70 B-body rear end is 60 1/8" drum to drum... 3" wider than A-body... 1 1/2" wider on each side