Andy,
Something that worries me, with US vehicles, is the retention of the original rear lamp units. Back when the vehicles were new, the speed limits (in UK at least) was 30 mph and 20 mph for lorries. These lights are not large enough for modern day use. When I restore vehicles, I pay particular attention to the size and position of rear/stop lights and indicators. Accepted that they may not look authentic........but on the road, self-preservation is utmost.
It would appear in this case, from what has been said, that one of the vehicles must have stopped quick and the Chev C60 could not stop in time.
It gives us all food for thought.