55.2-59 Different front shackle years ?

[Hcb3200]

I am replacing the shackles on the front leaf springs when I redo my springs in next couple of weeks.
But when ordering I have found conflicting info.
This is the 1956 Chevy 3200 project.

I see online some say 55-56 and 57-59 two different shackles and others say 55-59 some even say 47-59.

So the real question is are there specific differences between 55-56 and 57-59?

And a side note if you guys have a good spare set I might be buying.