[Kurt S]

Clippinger ordered at least 2 other L78 cars, built at the same time as your car, and were also dark green. One is a possible dealer modified car.
Your car would not have received an L78 from the factory, especially since 2 L78's were actually ordered at the same time and both are 4K cars.
So the dealer only tried to save money on your car and not the others? That's not how the ordering process worked - either a L48 engine or an L78 engine was ordered and the proper body was then built.
As a SS350 car, I would question that your car was dealer converted to a 427 car, especially that late in the year. They would start with a big block, normally an L78 so they could reuse the most components. And have the right engine mounts, heater core, radiator, etc.
And your car 124377L157826 still has a SB heater core.