[67ChevyRedneck]

Based on my modern experience, what would have likely happened was GM had the design complete, the testing/mules done, equipment and suppliers lined up, and they would have shut the plant down sometime around August/September 1970 to retool and organize the plant for the changes, again, this was a significant change. They would have likely reopened the plant after the tooling/process changes were made a couple weeks? later and started doing training with a reduced line speed on the new 1971 model trucks. Because this was a significant change, the chance of "left over" 1970 model grilles (and hoods, remember the 69/70 emblem was in the hood with holes for it!), etc being put on a "new" 1971 truck would be extremely rare in my opinion. *If* GM never shut the line down and made changes as the line continued to run (which I think would be extremely unlikely given the complexity of the change) is when you could end up with a mix of trucks/mistakes. But again, it would be a very limited small number of trucks with a high 1970 production number and not something that was offered as an "option."

A more likely explanation of a "1970" with disc brakes would be a 1971 truck (I'd assume a correct 1971 front clip) that was built from September - December 1970 that had VIN stamping error (unlikely, but has shown up here) or what was much more likely was a title/year error by the DMV assuming the "new " 1971 truck was still a 1970 model being it was registered in 1970 still.