Blind Driver, I would not adjust the rear ride height. The alignment on the axles is set for the ride height from the factory. If you lower it say 2" then you just un-aligned your trailer. Also, your air bags may bottom out or you can cause damage to the suspension since the bags are made to operate at a certain PSI when under a load. And you are able to haul 10' with your step. Just remember that of the load is 10' sitting on the ground, you don't want to place any dunnage under it. I've seen a few guys be at 14' high because they put a 4x4 under a 10' tall load.
Ooops I met a driver with a measuring stick. It was a expanding square pole with a lever at the top end. The pole was marked every 1/2". It was really neat, but it was also $80. I don't haul over height too often.
I don't know if they sell them in the store. Besides, I'm just a lowly driver with dreams of owning a truck someday
My step has the tires sticking above the trailer 4". So this makes me have a hump for the fenders above the tires, but makes my main deck 32" off the ground. You also flip the switch and drop your trailer when you hit the scale lane, just to keep from hitting the over-height eye.
The title says Evans, but the only thing thats OEM is the frame. Its a 84' that has had everything done to it. It started as spring then I found some nice used low ride air and installed that. I run the 275/70's on it because they hold 6050 per tire for when I need to run heavier than the 20,000lbs. per axle.
i'd make a home made tool. like a 13.6 peice of wood. and put a 4 foot peice at a 90 degree angle. or some rebar or something. you don't really need a measureing stick. you just need to know if the load is higher then 13.6 on the east side. 14 on the west. i haul equipment all the time that isn't permitted. so it has to be adjusted somehow to meet the height. if you haul a lot of taller permiiteed loads. then i can see needing a measuring stick. cuz you need the exact height for the permit. i hauled some bobcats from michigan. they have a problem with drivers hitting bridges. i told him the same thing. make something up so they have a measuring tool. and no more damaged equipment.