A few things I can shed some light on. I worked for Chrysler and GM in parts for over 20 years and on many levels they would use different part number for the same item. For an example that I’m sure you have seen is a casting number on a part verse the part number in a book….two different numbers for the same part. There was many reasons for this but I can tell you first hand it will confuse the day light out of you. In all the paper work I have for these cars ( from Sept 1 1967 to May 1968 ) there are many inconsistencies when it comes to part numbers so I have found in the early days of these notes that the description trumps the number and if the number is correct then it’s an added bonus.
I know there were two seats. A fixed back seat and a folding seat. I BELIEVE the Van A100 had a fixed back and the pick up style A100 had a folding. I BELIEVE we’re Bob wrote “A990” above the part number is the seat that he wanted to use and that was a fixed back seat. Did a some cars come with folding seats?…maybe. To me it’s not necessary what the car came with, it is what the car should have, UNLESS you have overwhelming proof of something different.