have you seen this before???

[Wildstreak]

So somewhere along the way my dad found a nice 67-72 parts truck and decided to bring it home and add to the collection. After seeing the truck I was amazed to see a tool box built right into the box(not sure if its a tool box, just what I call it for now). I have seen this once before on a friend of a friends truck, it seams my dad bought the truck from him and it was his parts truck for that build.
Pretty much my question is, when were the boxes produced, if at all and how rare are they???

I've enclosed a pic, any info is greatly appreciated!