I'm sure none of these are exactly the same engine, for one thing they are all steam (just to keep it relevant to Cyclone, sorta). But these are just a tiny selection of wobbler engines that basically embody many of the traits of the Duke engine. Similar gasoline "barrel engine" designs had a period of vogue in the 20's and 30's with an effort to reduce frontal resistance. That none of these was successful in the market might make one wonder.