Stock LT1 head Chamber volume

I'm trying to lower CR by increasing the chamber volume on stock LT1 heads. The stock heads are supposed to be 54cc. Anyone know how much they can be hogged out. I'm trying to get down to 9.5 to 1 (I think about 72cc) without pulling the bottom-end. Am I dreaming? :confused:

Thanks in advance, TJ

With a little better math, it looks like I've just got to get to 64cc or so...