I am intrested in making one too. I have been pondering on getting a lathe/ mill combo machine for this. I think I wll try to duplicate the OS FSR type because of the seperate crank and piston housings for ease of machineing. I am realy interested in four strokes and looking at both these designes to start with.

http://www.littlelocos.com

I think the single made a little bigger would work and I would like to make the radial for small WW1 models.

Tom