the extension panel is what I am thinking would have to be different (at least on the 6000 series).
I don't think the 4000, 6000 Series would use a panel extension like the 8000, 10000 used, as the heal of the stock fender curves down into the rocker molding (nothing to bolt to). I'm thinking the smaller trucks would have used a piece of strap metal as a front brace, bolted to the fender lip and outer corner of the running board, but that's just a guess by me.
Mike B
