On pickup trucks,If the seat is original ,look in the back side of it,I have found a few build sheets stuffed under the springs...also saw one truck that had it stuck to the rear cab wall under the rear window,hidden by a cardboard liner..On a K5 though,it may be hidden anywhere..A few I've owned had it glued to the drivers side inner fender under the hood...
I found the build sheet for my 81 G-10 van stuffed up inside the unibody frame rail near the sway bar one day when I was lying under it changing the oil--saw a hunk of paper hanging out of the hole,thought it was money at first--was surprised when I fished it out and could still read most of it,this was when the van was at least 20 years old!..