I will follow this with interest as I have a similar build plan with an F-450. You already have folks with similar builds chiming in, that's great. I watched the Muse Roamer YT videos. Unfortunate that he realized after he built his frame and shell that he did not account for wheel wells and had to modify his frame. I'm guessing you will go to a Super Single to replace the duals? What kind of overall weight do you think you will be at? Over the rear axle? With the new 10 speed transmission do you believe you will have to regear using the 40 - 41 inch tires and a gas engine?
As for the lift I like the Carli suspension setup. While their site does not mention the F450/F550 CJC Offroad does now offer a kit for the F450 using Carli components.
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Carli does have a long travel airbag but it's limited to 2,000 lbs.