Can I do this with filler neck mod?

[glovemeister]

I bought the supplies to do the regular mod, but on my pickup its just not gonna work as i have a flatbed. To make it work I would have to reduce slope on my filler necks and that simply would fix the issue. Could I replace the rollover valve with a different one and then use 5/8 hose instead of the 1/4 inch on there as long as I routed the hose at or above the slope of my filler neck?

Presently for my front tank i have the roll over hose clipped to a beam on the bottom side of my flatty with some steep angle on it. It seems to work good as I removed the plug in the end of the hose but I wonder if it would work better if it was 5/8 instead of 1/4 hose?