I think it confirms I have something different. Maybe a mod, repair or whatever. I've got the mount bolts/washer assy out but the rivit is installed in the bottom of the channel,inboard of the mounts about +-12 inches. Goes thru the floor support and attaches to a bracket on the frame. It is rusted but looks like a big old bridge rivet(1/4-3/8). Pan head on top, swedged on underside. If its not OEM maybe I should just cut it off and forget about it. Thing is I been around this truck for a long time and its never been wrecked or cab off. Strange !!
Thanks for the help.
Bob
