The 3 cylinder radial engine shown in the link
was constructed from plans purchased from Littlelocos in the USA. The video shows it running pretty well. At low speeds it has that beautiful throbbing sound typical of a radial. The most difficult part to machine I found was the crankshaft which has a gear machined unto it. This gear runs on two planet gears that drives the cam at slower speed. The cylinder heads were also difficult having the valve trains sitting at angles to leave little space for error.