Just been through this exact saga myself.
26 Crank, rods and pistons. CP pistons at 86.5 bore have 15.5~cc dome. My NEO head was 54cc, And I had originally bought a 1.2mm gasket. (nearly 11:1CR from memory)
Long story short I had the head taken out to 57cc and added a 1.8mm gasket which landed me at 9.3:1CR.