As far as I know, there's no genuine headless Webkit.
For a genuinely headless system, consider Chris Lord's "offscreen" branch of Gecko, discussed here: http://blog.mozilla.com/ted/2010/07/29/moz-headless-screensh...
I'd be interested in sponsoring someone who wanted to bring the offscreen branch up to mainline, and Chris would be willing to mentor you in such an effort.