Has anyone had direct experience importing a non-EPA engine to the US for an aircraft application without it getting confiscated by the EPA or customs?
I have not, but I had a friend buy a Mercedes G Wagon for parts from England. Right hand drive. Had engine removed. Car shipped on one boat. Engine shipped on another. Originally they were brought in for parts but in the end they were reunited. Not really any issue. They sell Japanese market engines all the time in the US.
As long as its for off road use there are no EPA rules to follow. If anything, import it as parts as 'spares' in multiple shipments. You could Fed-Ex it to your home.