I type slow, and get interrupted often, so Rusty_OToole beat me to some of this.
What made Henry's V8 special was that it was the first major production single cast mono-block V8. All that in one package made it the first economically cheap V8 available to people of modest means. Other than the low cost (Henry's real specialty!), there "arguably" was nothing really special about Ford's V8.
Would it surprise you to know that a V8 was designed and built for automotive use before a straight 8? The idea was proposed and patented in Europe soon after 1900. A handful of V8 engines were installed and used in European automobiles before 1907, although many more V8s were even then being used in Speed boats and aeroplanes.
One of the first V8 engines built for use in an automobile in the United states was then installed in a specially built motorcycle frame for testing. I don't have the article in front of me, but Floyd Clymer mentioned it and had quite an article and photos about it in one of his books many years ago. If I recall correctly, it was a bit before 1910.
Cadillac is of course usually credited with the first production V8 engine in a production automobile, late in calendar year 1914 for the 1915 model year. More serious recent research suggests that Cole likely beat them to the punch. Certainly, Cadillac was not alone with their V8 engine in the mid 1910s.
I don't know just when the first industrial and marine straight 8s were built? However I know some were around about 1910 (I would suspect some earlier?). Automotive straight 8s didn't come around until about the late 1910s. First in racing specials, followed by exotic (by 1920 standards) sporting automobiles like Duesenberg.