Just finished drawing up a simple mill engine, I've tried to design it so that it can be made using a lathe and a drill, no milling is required.
I've also tried to make it so that the cylinder can be used in other engine configurations.
I wont be making this engine for quite some time as I'm going to be concentrating on other things but if any one wants a PDF copy of the drawing just send me a PM with yur email adress and I'll send them a copy.
Attached is the assembly drawing
Stew