C.R. on the B18 is set by the thickness of the head and not the gasket, which is the same for all. Using a "thin" gasket will raise the compression. The only way you can lower it is to use another head which is thicker unless you want to do some headwork and remove some metal around the valves etc. Unless you have the tools and expertise, that's best left to someone who knows these heads and knows what they are doing. I'm sure that another head can be found for not much money. Have inserts for lead free done while you're at it.