How far can I safely mill a 360 J head?

I plan to mill my heads for my 360, but I am unsure of how far to go.
Has anyone tired this with success, is there an area to stay close too for best power?
Also, I then assume you also have to shave off the intake side as well? .0123 for every .010?

On a budget what are the main things to have done to the head?

Thanks!