I've seen an Arrow Sport and heard it run. It wasn't airworthy, though. Believe me, I looked at using a Guzzi power plant. Turn it upside down and use a dry sump.
But.
Without a reduction drive, it would be limited to 3400 rpm by the prop, and Guzzis need 5500. I *have* a Guzzi reduction drive, but it adds too much weight.