Kz1000G1 Pistons

Just bought a very used Kz1000G1 and am doing a top end on it. I was quite sure that the motor had never been apart but when I removed the cylinder head surprise, surprise, the pistons were stamped .50. Any ideas?

They are .020" oversize

Thanks APE, its a little confusing, I am installing a Wisco 1045 Kit.