I think that ~3" is about all you're going to get without major modification. You'll have to notch the body mount on that side to mount the box.
I'm still kicking around how I'm going to go about it. I'm moving my coil buckets, shock towers (though it's looking like I'll build some hoops), and box forward. I'll get a new lower steering shaft.
I'm also moving my coil bucket up a couple of inches. I want nice long springs, and a low stance. I'm also going to look at BB/F150 buckets, and see if they may work for me as well. There's also a chance I'll wind up building my own. I don't know yet.