I did it all- had cat set the timing/fuel timing, replaced all the hoses/belts/thermostats/boiled out my aftercooler and gear cooler, pressure tested them, filters, fluids, some paint etc.. was a huge job. I replaced my exhaust risers with dry units because the factory design is such that if the inner wall of it fails, water is leaking back into the turbos and potentially causing big problems. I would check this first and then definitely make sure you cooling systems are in good shape (engines should run low 180’s at cruise). Also make sure it turns full 2800 at WOT or a hair more. I am a nut a bout preventative maintenance so you dont need to do all of this but the cooling system is the most important system not he engine in my opinion. Suffer one overheat and you could be looking for new engines. Deal with the aftercoolers and gear coolers, make sure the impellers and thermostats (fluids and filters of course too) are in good shape and you should be fine. The rest is for the paranoid. These engines are fantastic by the way. Quick start up, no smoke or soot at all, none. Run Cat 30wt oil and you should have the same performance. I like to cruise them a little below 2300 because they are so much quieter than at 2400 but the EGT’s dont care. Once on a plane they get lower the faster you go so I think the engines are very well paired with the hull. Lets see the boat!