In 3 of my books say its 0.0048" for 1cc on 340/360 heads so 0.060" would be 12.5cc but I've never measured any of this for myself so you could be right.
Well.....everything I've read or seen discussed says like .0067 for 1cc. BUT, the absolute best thing to do is CC first, then mill X amount and CC again. See, the thing is this. Different shaped chambers have different amounts to make the same changes. If that makes sense. I've done this very procedure in the past and HAD the formula.....but that was a long time ago. Crap doesn't stick with me like it used to. LOL