Milling 318 Heads to raise CR

My 318 is rated at 8.5:1 from the factory. I've been told the actual compression was closer to 8.0:1. I'm just going to cc the heads today and see what I'm actually at. So I'm going to be safe milling 30 thous without worrying about the top end going boom? Hmmm, maybe I'll mill 50 thous and use the 30 thous rocker post shims from Mancini's. . . . I just want to get my ratio up to a solid 9.0:1 actual compression or its going to run bad with my comp 268 cam.