Fellow 6.0 owner here, we have only had our van (2006, 200k miles) for about a year now. I had a lot of reservations about the 6.0 before purchasing but when I found the right van (I.e. all other non-engine specs, right price, etc) and it had a 6.0, convinced myself with copious hours scouring the internet that if I was willing to put the money into an engine-out bulletproofing and head studs that it was a good reliable engine. So right after our purchase we put about $12k into that bulletproofing process (link here
) and have put about 10,000 miles on the engine since. Although we have had a couple of issues with the van in that time, neither was related to the diesel (faulty wiring harness and a brake booster). I live in Phoenix, so the heat is something I have to constantly be cognizant of, but the van and I are getting to the point where I think we really like each other
We have two small kids, and the hum of that engine actually puts them both to sleep on long road trips - to the point where its when we stop that they wake up. The mileage is decent for a huge van like ours, and I just plan to stay on top of fluids above and beyond what is recommended. Not being my daily driver, my biggest challenge is just to make sure that I give the van regular exercise as I know they don't like to sit. 10,000 miles isn't a lot of miles, so I guess the jury is out somewhat, but so far so good.
I would second something that others have said - there's a LOT of value in knowing what you have. The bulletproofing/head studs is something thousands of others have been through with success. Once you get that done, you should feel pretty good about the engine itself. Tackling some other engine swap seems scary to me, like a whole new can of worms. I wouldn't want to blaze a new trail if it were me. If you go the bulletproofing route, give the link that I posted a read - I got a lot of great advice from others on the forum on what to do while the engine is out. Then you're starting with a basically new engine the way that Ford should have
designed it in the first place. Taking care of any leaks you have at the same time should be easy.
My two cents