7.3 is overbored 6.9?? Doubtful

A volumetric change that small, .4 L, can be achieved many ways and the easiest would be to very slightly increase stroke length.

The 7.3L engine is based on a production block, Internationals T444e. That engine has been around for many years and is essentially bullet proof.

Cavitation is a problem seen in many diesel engines not just the 7.3 PSD.