My 69 coupe (small block) been in the family since 1972, found no build sheet, found little under the carpets. Some change but was probably dropped out of my dad's pocket, moms purse, sisters purse.... The funny one was when I took apart the rear end and there was this small red plastic cap in the gear lube! I called a buddy who worked for decades for Ford. Yep, he knew what it was. When they changed out the lube for filling the rear ends, they often ignored the step to "twist off the plastic cap and discard". He figured the coupe was on the line when they were changing out the lube and they just shot that cap into the rear end. Interesting thing was that it wasn't torn up much at all.
Now the 1970 Mach, 428 CJ....Found under the front passenger, a baggie with spare screws, wire clips, a door switch even. Under the rear seat carpet by the tunnel, a good build sheet, parts of a build sheet under the carpet at drivers seat. But the funny thing was, well remember 1969 and 1970, when everyone was going to the craft store, buying up these little beads and stringing our own "hippie" beads? There must have been a few hundred under that back seat. Now just what do you suppose was going on in the back seat that some hippie beads got busted in the back seat? I'll wait....LOL