Here's a chart. Rear End Widths
Note the S-10 7.5 rr is not on there, it's 56" and suitable for only low-hp...but common. Most of the narrower factory rears that can support power (Maverick or Mustang II 8", Mopar A-body 8 3/4) have been picked or scrapped years ago so happy hunting. Btw all are measured from the wheel-mounting flanges.