[Bobcat]

I forgot to answer your important question. I have no idea where you saw brackets and VIN's on enigines in the pre computer age. But the Pontiac plant used a guy by the name of Emanuel Labor. He would wait until the already installed drive train suspension etc. was about to be mated to the now desending body shell. ON the body cowl would be a paper with punch marks and a VIN number. He would set his metal hand punch and first head to the left rear frame behind the wheel arch, top rail and punch in that VIN number, as his cousin Manuel Labor would punch the same VIN number into the block. There would also be a VIN punched into the firewall behind the heater box as the body was mounted onto the frame. As the unit went down the line others would read the cowl sheet, frame sheet, interior sheet trunk sheet and put the other door post or dash VIN in with star rivets and the items, OLD CONCEPT here, would be read Manual and Emanuals cousins down the line. While at their respective places they read the sheet and hand pick from the bins behind them the item/ brackets needed to hand assemble the car. Wrong engine, right VIN #. Too simple isn't it.
There is a new book at Borders and Barns and Noble in their Automotive section showing the old assembly line and just how the lines ran. Go thumb through it, it's fasinating for people who are not firmiliar with auto plant manufacturing. It will hopefully help you better understand.
I'm affraid to even tell you about the foreman that would walk cars down the line to make sure options not ordered were put on cars for VIP's or friends. Or in the case of many special Royal Pontiac cars, they made sure that sound deadening and dumb dumb where omitted. And no, these were not caught in final inspection back than. No one had time to look over the entire list. And NO Jim Mattison would NOT have record of this in his Historic Services.
The inspectors just made sure the cars ran off the line. Only one in maybe 20 cars probably more where pulled for assembly quality inspection and moved into the 100% (Reliablity) garage behind the plant. That was more for defects than to catch add ons. Like miss matched shocks. Leaky intakes, not working heaters, lights or air conditoning. The guards would just make sure that nothing loose was in the cars unless they saw hand written instuctions, like headers in trunk for the '67 Z-28's.