There are quite a few "kit" engines to include radials that you can print and assemble posted on http://www.thingiverse.com/ While I have printing down pretty good and have a decent printer the design stuff is still a pretty weak skill of mine, so I am hoping someone will post the .stl used to make that engine. Of course they don't run (although you could make a C02 one functional) but they make a nice display.