Those covers look really nice.
As for an EHS style lid. I made one for my old 87 Warrior 350. I cut out a piece of aluminum for the frame and then fit it on the air box and then drilled all the bolt holes and bolted it down, Then I cut the plastic with it all together so it would be a nice clean cut and make sure it matched the aluminum plate. Then I just cut a piece of outerwears to fit. Worked pretty good.
2008 700XX - OMF Beadlocks w/Billet Centers & Reinforcement Rings, Kenda Kutters, CCP Steering Stabilizer, ASV F3 Levers, ODI Rouge lock-on grips, Houser Bounce Nerf Bars, Pro Armor skid pad, UNI Filter
2007 400EX - CCP Steering Stabilizer, GT Thunder 450R Shocks, 450R Rear Brake Conversion, YFZ450 Front Brake Conversion, ProTaper Bars, Rath Racing Nerf Bars, Alba Elite Bumper, ASV F3 Levers, ODI Rouge lock-on grips, UNI Filter, Kenda Kutters, Pro Armor skid pad, Armadillo Swing Arm skid pad