It could be an ‘aftermarket change’ as you suggested, but that still does not explain how my vin/ serial number is suppose to be for a late series cab but all the evidence I have shows this is an early model cab from the factory.
i am also going to measure the hinges, as mine dont look as long/ different in lengths as yours. I might have to remove a door to look at the hinges and see what the hidden part looks like.
Given all the data we have, and the fact no one has seen this configuration before, I would say odds are high this was not a factory configuration. I guess we may not know more details until I get brave enough to take the cab and doors down to bare metal.