Many times we will take a car and retrofit facelifts to an existing production model. That is why you could end up with a 70 body and 74 bumpers.
I did not see this article, but it sure brings up a lot of questions.
The tooling grid marks are for allignment in design grid position. It is not uncommon to scribe lines every 100mm and take a position point. This was for allignment and for checking build tolerance. It also helped the engineering team find where discrepancies are from the data to the real thing are- (The data was then drawings, now Catia at Chrysler)
We call these S1s/S2s. They signify a pre-production model at a feasibility "gate"
How this car could have survived is beyond me.
The process is similiar to what we do today. We put the car on a plate and we have a grid mark that we verify as gospel, then we retrofit new parts.
Dan