RE: OS 108 head gaskets...
With any O.S. Max engine, if the cylinder head is properly-tightened, that is, evenly, then the single gasket is enough. A copper gasket isn't needed. The stock one is just fine. Using two gaskets will reduce the compression ratio a bit, and may cause some power loss, depending upon how the engine's run.
The main cause of cylinder head gasket leakage is an unevenly-tightened cylinder head.