Comment by CraigJPerry

The thing that's missing here that really drastically changes the story is all the emissions control hardware that would exist on such an engine.

This is a circa 1990s engine in the US market i think? Dual Overhead Cam didn't really become popular in the US market until then i think. 70s-80s for single overhead cam to become established.

The diagrams are beautiful and informative as always from this author.