There is one rod brace that goes from the frame to the outer rear wheel opening. That and the running boards would basically locate the fenders. I believe the second bolt hole from the bottom on front and rear of the fender mount flange would be at the same height, as they line up with the bed angle on the bedside and bolt thru them just above the wood bed floor. I don't have the height of that point above the frame, but could probably track it down from my bedsides in the garage.
In regards to the two holes 'second from the bottom' that Kevin references above, would anyone have any measurements for how high to mount them and where left to right? I have a homemade bed, so I can't really us any references to an original bed. Perhaps from the axle itself? I'm assuming a 3600 would sit in reference to an axle the same as a 3100?
