It's been my understanding that engine paint, unlike body paint, was not an exactly formulated and controlled product. It was probably purchased from different vendors based on cost. If someone offered paint that kind of looked half right at a lower price, that was the color that was used until the vendor mixed up a new batch or a cheaper vendor came along. Like I said, that's MY understanding. Most of the restoration vendors sell the "correct" color, but you might find some more to your liking than others.