Elmer Wall designed this little 4 cycle gasoline engine back in the 1930's and the plans were offered in magazines, several in fact the latest being around 1952, several years after Elmer's death.  The engine is a relatively easy build but like all small gasoline engines requires attention to detail and high accuracy in finishing and fitting the internal parts.  The result will be a beautiful small engine to power your model boat or car and it will repay your efforts with tons of personal satisfaction.  The entire engine is detailed in the construction article and the castings could be easily produced in aluminum and bronze from patterns made from the drawing details if you have the ability to produce non-ferrous castings in your shop, all the castings are quite small so only a small melting furnace would be required for melting.