narrowing a b-body rear

That chart is wrong. A-body 8 3/4's are 52 5/8" flange to flange. Perch centers are 43". According to Dr Diff, you can narrow the housing down to a minimum of 51 1/4" using his 1/2 offset hanger kit. Any shorter then that, and the outer U-bolts will be into the housing ends.

EDIT: I see you changed the link...