You will have to read the ad a little closer as it is a little misleading. The piston,cams and gasket are 649 and the ported head is 425, which since I called ALBA and they were to busy to talk, would be my take on the ad. I am sure that the ported head would have to be either yours or for an exchange.
I would be interested in knowing for sure though! Since the ad also identifies it as a high compression piston and doesn't mention anything about increasing the cc's you will have to run race gas and even at that 20 HP is close to a 70% boost which I find hard to believe.