55-59 bed questions

[Longstep70]

So I have a couple of questions about the beds for 55-59 trucks.
I'm currently looking for a 55-59 truck after previously owning a '70 so bear with me if I ask something obvious, its all part of the learning curve...
First off is the topic of interchangeability. Are the step bed sides, fenders, front panel and tailgate the same as the ones used in later years? Fenders on 60-66 look awful similar. I have the bed box for a '70 step and these parts look the same or very similar to the 55-59 stepside parts too. Are they the same?
Fleetside beds on the 55-59 seem to be less common than the steppers, are they more valuable? I don't seem to be seeing much, if any difference in prices for fleetsides over stepsides.

-Andy