The later model 6.0 (05-07) had a lot of the issues taken care of. There were something like two dozen updates between 03 and 07.
The E series 6.0 is detuned compared to the trucks, but the engines are identical.
You will need to build or buy a cab panel to cover up the walk through in the back. IIRC there is a company that makes them, they're not too expensive.
There was a 7.3 ex ambulance locally that I was thinking about buying, but with no 4x4 and the issues that it had made me pass.
The good about an ambulance, they get strict maintenance and repairs. The bad, they get ran hard and a ton of idle hours.
Vans are a booger to work on, BTW.