Can't answer your question... but from what I've read, you'd be looking at a ton of work for a mediocre end results. For the Effort, I'd be contacting U-Joint or MG Metalworks... or Weld Tech for 2WD.
What I do know is that a complete 2001 E350 front end bolted directly onto my 12/96 E350 with no differences. I just don't know how different an E250 is From an E350... likely not much. Although the 7.3 is going to be very heavy for the springs from under a 5.4. Agile Off Road has a kit to fix that as well as some of the other Quigley Limitations.