Goldstirling

Like all the Goldstirling engines there are a lot of curves. The engine could be built using rectangular pieces as well. the only important dimensions are between hole centers.

The mostly full size plans for this engine are $30. When ordered with another set the price is only $50. This offer includes the quad-rocker engine too. 

This engine looks a little complicated, but it is just a horizontal engine with the flywheel on top. Most of the parts on this engine are just for show, but when it fires up there is a lot metal moving around.