Engine plant. I could see a longer gap if SCJ cars were built in batches but not a shorter gap. Just a thought. In other words if I'm not clear some of the reasons I have heard/thought were cars being early or late from their scheduled build dates were due to being how common a car might be for all parts to be available on the day of production. So say they have to wait for a batch of SCJ engines a car's build might be delayed until a batch of SCJ engines show up.
I'm open to what anyone knows on why some cars were built way behind schedule. Color, parts etc. I also understand rotation of supplied parts were never 100 percent perfect.
Its a bit difficult to talk about delays or issues through out the whole production years since there are so many "moving parts" For Job #1 if I recall correctly and would have to look for the documents, but don't believe that SCJ were not ready for Job #1 so all of the early orders would be delayed since the engine had not be full checked out, blessed and trouble free at that point. Problems with the high gears and overheating appear to be the challenge and it appears why they would eventually require the oil cooler
Though scheduled for build earlier those orders didn't get built to Oct 68 or beyond. There appears to be a handful of cars that got through every early somehow maybe as test or promotional units. Looking back we also have to take into consideration the type of order and the back log created by this mess. It took a while to catch up since the car plant wasn't going to built the cars in "batches" and I'm not sure how much lead time the engine plant had.
Of course the CJ site has had a number of long running threads on the "earliest" SCJ and subject like that going back over a decade