I noticed the same thing on my last communication with the factory. The intake diffuser is available seperatley for the regular 58cc engine. There are now factory built headers available for the 58cc engines as well. It is my feeling that the change in con-rod and bearing was done to provide some cross-product compatability with the new 116cc boxer engine. The "Prosport" version of the engine will cost about 10% more than the standard 58.