I'm not surprised because 1955 is the turning point because it was the mouse motor that dethroned the flathead and it took a few years for it to really catch on. After that, there was no looking back.
I'll bet some of the regulars here would love to find one of the replacement heads shown in the article for an old straight eight and build one of those up for a hot rod of some sort, perhaps using a longer than typical frame from some larger car to make room for the extra length of the engine. You just don't see straight eights used being used all that much in hot rods so it could be a real stand-out.
I think that the finned aluminum flathead head (4-6-8 cyl.+V-8) was about the single most appealing speed part ever produced.