Jeff -- I'm not sure what you mean by "Must have taken time to do it by hand originally."
My contention is that this is the machine could have been used at time if you were a supplier of the larger and longer harnesses.
The machine was in general use from the 50s through the 70s.
I can see where the short harnesses (and your gas station story is certainly telling there) would be done by hand.
And the shorter portions of say, the main front harness on my 67, would be done by hand.
But if one were cranking thousands of these, the long sections from the firewall forward looks too perfect to be done by an unaided human. And would take too much time.
Just another thought . . .