Do what you are comfortable with, but I got my info/instruction for headspacing from what I thought was a fairly reputable source:

http://www.youtube.com/watch?v=KICBv-0U87Y

Sponsored by accurate shooter website and I assume since this guy owns the machinery he does and is apparently making a custom bench gun for someone else he would use a safe method of headspacing. Once again, I am far from an expert, in fact am just a beginner, but that is my .02 and what worked for me. Of course do what you are comfortable with and usgunner is right, this is not something where "close enough" is good enough, there are some serious side effects, from a broken gun to broken body parts if things aren't done properly.