stock valve springs do pretty good with bigger turbos, as you don't have as much exhaust pressure trying to blow them back openAny valve train mods needed to run at 4800 rpms for hours on end?
stock oil pump/drive gear is better than the faster brm one which some people have had cavitate at higher RPM
on the lag, a couple seconds' lag ain't bad on a marine engine because you've only got the one gear. With decently done up maps it'll come on (and not wreck anything) lugging it at 2k RPM. One of the magical things of turbochargers is that attribute, they aren't connected to the crank so they'll come up to speed at basically any engine RPM.
People here are overly sensitive to it because pretty much everyone runs a manual trans in a lightweight car.
ETA: my comment of the turbo waking up eventually at 2k is not to mean you should be setting up your prop to live down there. unless you're happy with limiting it to less than stock hp output. Motor would not be happy with that kind of torque load at 100 percent duty cycle.