RE: Gas Engines
Don's Hobby Shop also has a book on giant planes and gas engines. Lot's of info in it.
Regarding ignition systems and component spacing. There are a lot of methods that work most of the time. The manufacturers try to provide installation information that should work all the time. When I have doubts or questions I seek out the people that design and make the ignitions, generally Terry Grant at CH Ignitions and Ralph Cunningham at RC Ignitions. There are several more that are specialists in their field that are well worth conversing with. Listen to them first.