Inside edge of the pickup fender to frame is 13" to 14", so just a bit wider than the panel.
53panel, re the 3:08 bottom end, not the greatest, around 3:50 would be ideal. In my case a friend had this rear end and FREE was right in my price range. It was 6 lug and very near the same width as the 57 pickup rear I took out. Here in this very flat land and my light weight 46 pickup (also 261) I can get by just fine with the 3:08, your panel may not like that ratio.
