I'm a Ford diesel owner for the last 20 years, and even I would say that you should take the money you'd spend on bullet proofing the 6.0, and put it towards a different truck.
I know that you can have good luck with a 6.0 after bullet proofing them, but there is the question of value. As stated before, unless you can do the work yourself, you will have put more money into the truck than it's worth. Even after bullet-proofing, the 6.0 resale values are pretty low for a diesel truck.
As far a s a replacement, just about anything would be an improvement, even an older 7.3L Ford. You can find good used examples with low mileage for under $25k.