57 Chevy Stepside Pickup Bed Rail Question.....

[JamLazyAss]

I'm brand new to this site, so please bear with me if this question has been previously asked.

I recently bought a mint 57 Chevy Stepside Pickup. It didn't have a box for some reason, but the guy I bought it from had found a nice one. It didn't have the cross rails, or wood. Otherwise it's complete.

Here is where my questions start.
I bought a small lot of cross rails locally for a steal of a deal.
When I got them home, I noticed that there are two small "blocks" under each rail. The spacing or location of these blocks are not all the same. Some are spaced wider than others.

Are these "blocks" supposed to rest on top of the frame?
The ones that are "closer" line up to the frame.
The "wider" ones just hang over it.

And finally, the cross section at the rear, where the tailgate stops against when closed, has two mount tabs. Again, I have two of these and they have the same spacing differences. Which is correct, the wider or the narrower?

I'll figure out how to do pictures next to make things a little easier.

But until then, any ideas???