Hi Russel. This may seem a little mid-eval but I've had good luck on othe steel pistons using this technique. I take the piston (no pin) and balance it on an aluminum bar. I put about 6oz of 10w30 in a soup can. I then take a torch and heat the piston carefully untill it becomes deep red all over. I then quench it in the oil. It should grow. I have revived quite a few engines this way.