The piston to deck clearance is crucial to knowing the compression ratio. The dish in those pistons are huge. I suspect that the compression is well below 9.5 to 1.
They do have a large dish, but look closely. Those are step dish pistons. See the flat on the intake side? It's taller then the rest of the top of the piston, so he may have a little more than you think. We won't know without some solid answers.
