Years ago I heard of a SS Racer(Dave Wren) having to weld up the top of a piston that was .120 thick, he had bougt a car that had those pistons in them and the previuos owner had mill and finshed the tops of the pistons. Dave had not done them that way intentionally, he siad they look like baseballs, with valve reliefs not like pistons he had run before they had passed tech in the tear down for the class win at that years Winternational