Buildsheet location and the possibility of finding one of the two or more dozen printed for each car from my experience seems to be dependent on year, plant and worker/shift.
For 68 Deaborn there would have one attached to the body front and back, possibly one located between the seat springs and burlap that make up one of the seat cushions, and possibly one under the carpet. You can sometimes find random examples on the back side of door panels or shoved inside a door or interior quarter panel trim panel that likely save the worker a walk to the trash can for his copy
Big block, small block or 6 cylinder would not be something that would have made a difference in this question