Heads question

As I mentioned in the original post, they have been cc'd to give me a more "streetable" 11.5:1 CR. The pistons are TRW 13:1 when used with stock heads. Funny thing was, when I bought the car the motor had these pistons installed with STOCK J heads; I often wonder how the car managed to run on pump gas (the guy I got it from had no idea these pistons were installed and probably ran leaded regular!) and managed not to blow head gaskets!