F-series fenders are slightly larger, and also round, where the vans are cropped squarish at the top. ATS initially sent me an F-series set by mistake. I didn't notice they were wrong until I went to mock them up.
The accent lines on the F-series and E-series actually match up perfect as far as spacing goes. But the accents are a slightly different profile. My dually fenders stick out far enough you can't see the original body. But sticking flares directly on the body would probably require some trimming of the body work.
Here's a good pic to show how close the body lines are. But they still aren't quite the same.