RE: RCGF Engines
The only thing "special" about those engines is a coat of blue paint (yes - paint) on the head.
Henry, Driesbabe, myself and others specifically told the factory not to apply it to our engines because it is not particularly good quality. It is also a potential source of contamination within the engines as the parts are painted (possibly without very good masking - who knows) prior to engine assembly. We told the factory that instead of applying paint, we want our engines bead blasted externally instead - this improves the cooling a lot as paint coatings can inhibit the heat transfer.
For the Plugs - the engines supplied by the factory to the suppliers up to the end of 2008 / beginning of 2009 (depending on which model) had the 14mm plugs. CM6 plugs were requested by us and became the standard to all suppliers after that time.
The factory will make different specifications for some of their "OEM" customers (Trading companies who get engines made but sold under their own names). These are similarly shaped externally but that is often where the similarity ends. (Especially with one particular chinese based trading company who sells similar shaped engines from time to time but with a very different QC inside) that is usually done because of "price negotiation" between those trading companies and the manufacturer.
Us genuine Western distributors have a different quality control altogether.