owning a duramax truck myself, I have thought about this quite a few times. It certainly isnt without its drawbacks, but the allure of having that much power should be able to mitigate them. I wouldn't imagine that the stock v-drive would be a good choice, the LMM will probably have almost twice the torque of the 8.1 so im not even sure if it would survive it. Torque is a much smaller factor in the acceleration of boats than in cars so you will probably want to have it geared up to convert the motor torque to prop hp, but this can also be done by changing the prop parameters - so you arent completely locked in once you chose your v-drive.
does the Kodiak LMM come with a DPF? it would be a nice to have on a lake boat to reduce the particulate matter added to the water, but it will also increase operating temperature, add some lag, and limit the maximum idling time.
typical lake boats are turned off when they are stationary whereas a diesel would be better off idling for a few min rather than being shut off and restarted, so a more robust starter would be a good idea (seeing as you should change it out for a marine one anyway) along with larger starting batteries and an upgraded alternator (marine) to charge the starting and auxiliary battery banks.
you also might want to consider a different type of fuel tank and water separator to reduce the amount of water in the fuel, this might also help reduce the amount that the fuel foams when it sloshes around if it becomes problematic.
Im sure I'll think of some more things later - but im excited to see how this progresses.