I was looking at a F450 4x4 ambo, no rust, crawl through, 6ft interior height with a blown 6.0. My trustworthy local mechanic talked me out of a Cummings swap. Too many things could go wrong. They had another customer that had another shop swap one and it never ran. They looked at it and couldn’t figure it out, neither could another mechanic shop before them. Ultimately, the auction went crazy high for a 10 year old truck that had to be towed away. I imagine switching an E series would be even trickier. Can it be done, yes. Would I spend the money to do it, no. Unless that UJOR 4x4 came with it. Of course ambo wiring can be tricky, not the first I’ve seen like that.
There's that, and do I really feel like doing all that too. Not really. It's just an option that's on the table.
Talk about getting off topic, only one answer to the question.
But there are several threads with build solutions.
Maybe look at a few of the successful cab and chassis camper manufacturers... like Tiger who have been doing it for years.
There's no way I'm paying $150k for a camper, or even $100k for a class c.
Honestly, I'm not a big fan of having a van note at all. But I do like the new 7.3 gas option. I haven't had a car note in over 10 years.
I can build a box / camper that's better than anything on the market, for a fraction of the price. The only exception would be earthroamer.
Most RV manufacturers have to build something that pleases the majority, and they have stuff that just doesn't work well. Like 3 way fridges, horrible bathrooms, inefficient furnaces, etc.... If you cut out all that stuff. Add a marine fridge, mini split A/C, cassette toilet, and webasto heater, you get a way more efficient package, at a lower cost.
Then you can run everything through a legit battery / solar system and be completely off grid, like earthroamer uses.
I'm almost tempted to just get a truck camper.