Perry Mick in Oregon built a Long Ez with a Masda engine and orginally a ducted fan. He removed the fan and now his performance is similar to my Long with Lycoming O-320 power. There was also a guy flying a KR-2 out of Flabob (RIR) with a 6 cylinder Corvair and called it his little P-51. I don't know if he is still flying it though.
Personally, after 40 years of flying, I stick with certified aircraft engines. Look through the NTSB accident reports for engine failures and you will see that it is a major contributor to crashes.
My two cents.
Steve