The K Suspension XJ gutter mounts clamp onto the Econoline rain gutters just fine. They don't have quite enough rise, so a flat bar laid across them will hit the top center of the roof, where it's domed up the highest. I don't see that as a big issue, just something to accommodate in the design. These things are super sturdy -- they're made out of 3/16" thick steel.
1990 E-250 Sportsmobile w/ penthouse top, converted when new by SMB Texas.