That's why you see so many small sh*tbox cars that nobody wants, sitting on lots. They have to make them so they can sell vehicles that people actually want and/or need to buy, to satisfy the stupid CAFE requirements.
On my Aspen, the theory I use is, it was built late in the model year so they put in the engine they had left available. No idea if it's true, but it's a guess. Cars have been built stranger ways, and almost always the late build ones. My dad's '62 Fury was built in early July of '62 and it has odd trim, kind of like a combination of Fury and Sport Fury all on one car. It has 4 taillights plus b/u lights where a Fury should have only 2 taillights along with the b/u lights. It's got a crap load of SS trim, and die cast trim. I've never seen another one, or a picture of one, that has that same trim. He thinks they were trying to use up all the extra parts before the '63's came out. BTW, he ordered the car new and still has it.