top 20 V8 engines of all time…

One of the parameters is historical significance?

The 331 beat the other manufacturers' overhead valves V8's into production by 3-4 years, leaving the other manufacturers scrambling. The 1G Hemi (in mass production) was used in everything from industrial to heavy truck to marine to cars. Not to mention it's race history. Or the basic principals of it's military history.

The small block Chevy can only lead the list by the idea that had been in mass production since 1955 with just a few "upgrades," the parts are widely available and inexpensive, and the size of it allows it to fit just about anywhere.

But before that was the flathead Ford V8's were ubiquitous in the same usage. Speed parts were widely available, inexpensive, and the size allowed it to be used in just about anything.