couple of quick points:
marinized engines are produced by gm, and sold to Indmar, Ilmoor, PCM, Merc, and VolvoPenta, whom put custom tunes, various HCI combos, and different dressings on them to make them unique.
here is GMs marine engine portfolio, and the suppliers they sell to:
The PCM Z- engines are 6.0Ls to the best of my knowledge. the above link would indicate that they are L96s.
To the end of marinization, it is my understanding that engines marinized from the GM factory use forged components in the rotating assembly with hi-po, race oriented bearings and oil pumps because the expected average operating RPM is much higher than that of the same exact engine used in passenger vehicle. if you are going to swap in a salvage yard block, you may keep that in mind, with the additional precautions of ensuring that all electrical components are shielded against spark as most nautical engine compartments harbor explosive gases.
and for those that like to get in a pissing match about my brand uses pcm vs your brand uses indmar so my dad is cooler than yours....all of our engines start their life in same GM factory. none of the suppliers build their own engines....