Are there rear shackle difference? A B E body?

[khuebner250]

I can't find this info? I see A body rear shackles and B&E shackles. But I also see A B & E shackles. I see 4" center on center Shackles and 3.5" shackles. WTH? Any insight.
Keith

 

[Marcohotrod]

a is 1/2" bolt. b and e are 9/16" . stock length ?