Haven't found one for my 75K20 but I have both of them for my 70 LS6 Chevelle
"Both"? There were multiple build sheets used during assembly, so there could be as many as six or seven within a given vehicle.
Build sheets weren't really intentionally "stuffed" in the vehicle as Easter Eggs to be discovered by future historians. They were intended to facilitate the build only, and to be discarded at the end of the line along with any other trash (inspection/repair tickets, paper coffee cups, extra fasteners, etc). The reality was it was often easier to build the vehicle up around where ever the build sheet was laying which is why you often find them with sealer sprayed across them, screws shot through them, etc.
There were several build sheets used, each tailored to meet the needs of the specific area: Engine line, chassis line, interior trim, cushion room (seat build up), front end sheet metal, axle line, final line. Each of these areas is an opportunity for a build sheet to be left behind in the "usual" spots - on top of the fuel tank, behind door trim panels, above the headliner, under the carpet, stuck in the seat springs.
Vehicles are built with build sheets taped to strategic areas even today. Here is GM's most technically advanced vehicle - still built with a piece of paper hanging off the front.
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