If he was building an experimental amateur-built (E-AB) category airplane,
then there was likely no regulatory issue.
I have no idea how much these particular engines cost, but even at $100 a pop buying hundreds of them at once puts the applicability of "amateur" under some strain (or that of "experimental", TBH).OTOH, something about this story doesn't entirely make sense: who would get to the point they were ready to drop six figures on buying engines without, y'know, checking the regulations?