Hub stamping appears to indicate Q-1, also Cowley was a well known experimental airplane parts mfg. (canopies, etc.) in Mojave during the Quickie time frame. However, the pitch and diameter seems like it was for a larger engine than the original Onan???
https://losangeles.craigslist.org/lac/avo/d/los-angeles-authentic-42-inch-wooden/7762742096.html
https://losangeles.craigslist.org/lac/avo/d/los-angeles-authentic-42-inch-wooden/7762742096.html