Re: fender difference between light and medium duty
 

Width wise the 3000 series are 74.58 wide for most models and the 4000 series are 78.75 wide across the fenders. I don't know about hood fitment but since the extra width is with a lip on the outside of the fenders the fenders may well be the same.

GM heritage center pfd has most of the needed measurements This should be 57. https://www.gmheritagecenter.com/doc...olet-Truck.pdf

From what I am reading on the pfd the axle center line of 4000 series trucks is 2.5 inches to the rear of the axle center line on 3000 series trucks not forward. Someone would have to have access to both sizes of truck an measure from the front of the door to the center line of the axle/hub to tell though.