[RA1John]

With regards to the assembly plant worker making a mistake or assumption or the plant running out of parts and using whatever they had on hand...

Sure, things were different 50+ years ago at the typical assembly plant compared to today but it's not like they were building cars in their garage.
There were build orders, Broadcast Sheets (or Bingo, Tracking Tell-All sheets) taped to the body, engine, etc. with instructions for the Operator.
When the car came into a station, the Operator didn't simply make a judgment call based on what they felt was right, they installed parts per instructions.
There were also inspectors and material control. If they ran out of screws, someone didn't just run out to the hardware store for more.

Today of course, there are still Broadcast Sheets taped to the body and driveline components but there are also...
Sequenced parts, barcoding, pick-lights, Work Station Monitors displaying specific parts for vehicle in-station, vision validation, etc.
Mistakes still happen with putting the wrong part on car but nothing like 50 years ago when you could have a friend upgrade your axle.

All this to say... If survivor or original, un-tampered with Ram Air cars from '68 have a 4-blade steel fan, it's safe to say that is the fan used on all others.
(unless of course an option called for a different fan).

Then again..... Never say never, right?