NO, you cannot trust the early build 2003 6.0... My 2004 with leftover early build 2003 6.0 (quite possibly the worst engine ever put in any truck ever) has been bulletproofed and I still have problems with it, I can't trust it, and that's with 88,000 original miles... It's currently down again with another Crankshaft Position Sensor signal failure (either CMP sensor again or the pigtail/harness this time)... It's on it's 3rd Turbo, 2nd FICM, 2nd CKP sensor, 3rd set of Injectors, 2nd Injector harness, 2nd water pump, 2nd clutch fan (this time a 7.3 fan and adapter), 2nd Intercooler, 2nd set of CAC tubes/boots, 3rd VSS Sensor, 3rd ICP sensor, 2nd IPR sensor, 2nd engine (first blew at 31k miles due to failed injector)... IMHO, do not walk away from an early build 6.0, RUN AWAY FROM IT... As fast as you can, and don't look back... With this engine, once you fix any particular problem, it's not long before any one of myriads of known issues will creep up and you'll play the game of break down, fix, break down, fix, break down, fix, rinse, repeat until you finally throw in the towel and give up, but not until you have spent $$$ Thousands of dollars in the process... Don't believe me...? Take some time and search this "6.0 Engine and Drivetrain" forum and look at all the problems this engine has had over the years... If for some reason you decide to ignore this advice, first thing I would do is go out and buy the Autoenginuity Diagnostics Software, load it on a laptop and get real familiar with how to use it and how to diagnose your engine, 'cuz your gonna' spend a lot of time using it trying to troubleshoot all the problems you are going to have... I would also install a Scanguage II monitor, load all the additional PID's for the 6.0, and learn how to use the SCII to diagnose all the known issues when you break down 'cuz you are gonna' break down... It's not a matter of when, it's a matter of how often...
Some engines are just lemons. Even a remanned engine can be a problem. On another forum a member found a nut left in his oil cooler sump on his remanned engine. Unfortunately it happens .... way too often. That said, I believe it is still an extremely small percentage.
Not sure the 6.0L is any better or worse for those kind of problems.
Fuel pressure and clean fuel are critical to the injectors. Not sure I would be comfortable w/ the early 58v FICMS as you ran, but who knows if that contributed. 50 psig minimum at MAX load or WOT.
Making sure the turbo vanes don't stick (monitoring the boost and vgt % command as well as watching for smoke) is important.
Getting the right coolant in it is also critical - when the Ford Gold clogs up, things get hot (stuck turbos and overfueling can also get things hot) ..... and heat is a killer!
Using OEM sensors is critical. Aftermarket sensors fail WAY too often.
One thing not yet mentioned in this thread is that the 2003 and some 2004 had an issue w/ some wiring harness failures (chafing, etc). IMO those are the worst - hard to troubleshoot.
Personally, I think a 2003 could be a good purchase, but you have to do your homework (and then still you take some chances like any used vehicle purchase).