I looked into them a little while ago and liked 90% of the product. My biggest hesitation was making mounting brackets without having any knowledge of previous installs to go off of.
They do max out at 87in long. The cool thing is that they sell just the running boards, without a vehicle specific mount if you want to make your own. Or you can buy mounts and try and adapt them to fit. I reached out and asked if they had any knowledge about mounting to a E350 and never heard back.
https://www.ariesautomotive.com/part/3025183
I thought they were too pricey for an unknown. But I looked again and the price for just the running boards is closer to $1200.
Damn, I think I might be talking myself into these...