Jesse James and JRL Cycles built customs based around the Rotec 7 cylinder radial engine, now Paul Yang of IronGatsby Motorcycle has produced the Gatsby. I ran across this bike in the latest issue of Barnett's Magazine and according to the article, Yang has been working on this for 2 years so it sounds like these radial engine ideas popped up on the radar of some builders in a relatively short period of time.
The bike has 23 inch wheels on both ends and a CVT (continuously variable transmission). Looking through the photos in the magazine, it's difficult to figure out exactly how the exhaust is routed and the CVT setup is hidden pretty well, too.
Given the size and shape of the radial engine, it's a challenge to build a motorcycle around it, making it look halfway decent in the process is definitely a lot harder. Is this in any way a practical ride? Obviously not, but in the same way as the Jesse James creation and the JRL Cycles customs have shown, you can power a motorcycle with almost anything given a decent amount of time and fabrication skills. Interesting.
Link: IronGatsby Motorcycles