I like the drawing you posted. Normally the intake valves are noticeably larger than the exhaust. Cast iron rings are used in full size engines but I don't know what is used in small scale engines. I have seen some small engines use the bare bore of the aluminum rod on the crank, but I am unsure of the main bearings. If you search the web you will find out a lot of what you are looking for. One place I think is strictly IC but I don't have the web address.