You might want to look into the aftermarket radiator support.
Solving the Cracking Radiator Problem on the 6.4L Power Stroke
The later 6.0's were actually pretty decent. The head studs were updated. I kicked around buying a low mile 6.0 and "bullet proofing" it. To make a later 6.0 solid you just had to do the two things you'll be doing to your 6.4. I think you're going to be more than happy with the power and torque. Those things are a beast! Not quite 6.7L beast like but still...