I acquired a 57 big bearing complete rear axle housing for my 56 from a friend who's father had bought it new and noticed it did not have the rubber isolators on the leaf springs. He said the rear end had never been out of it. The spring perches had the small hole also instead of the larger hole where the rubber spring isolators fit, thses are just big enough for the bolt head of the center bolts the holds tie the springs together. Just curious what 57's got the isolators and which different. Were all rancheros without them?

Not sure what it is you have exactly. I'm assuming by "rear axle", you actually meant the complete 3rd member plus the leaf springs as well? The term axle is technically just the inside shaft that connects the rear pinion to the outer flange.
I'm not trying to be a correctness pita, just trying to get some answers for you. Myself, I can't see any reason why any '57 rear end would not have the leaf spring insulators. Yours probably just disintegrated over the years. Both the rubber and the steel encapsulator are available as reproductions.
Welcome to the forum, btw.
What part of our world do you live in?

Rich Muise, I edited the post. I am in Kansas.