Since you don't have your bed wood installed yet, you might consider widening the whole bed and inch or two. There was a former member here that did that to his stepside bed. I'll have to see if I can find his build thread.
Edit: I think his build thread here must be gone as I can not find it. This is the best I could do with a link to a thread elsewhere.
http://www.67-72chevytrucks.com/vboa...d.php?t=452520