I am guessing you would have to find a dealer that sell marine gas turbine engines and they should know a mechanic who would service them. There is a company that is putting out a Rotary Diesel engines that puts out 500 hp and weights 350 pounds. If you are going to high hp in cummins go to the C series it is designed for it. As far as outdrives go look up Konrad they make an excellent outdrive that can handle the torque the diesels put out. I am not sure Mercury makes a good drive that will stand up to the diesels. I have seen 6 or so Charter boats try the Mercury outdrives and everyone has switched to Konrad drives. The different boats had Bravo III's and Bravo II drives. I do not know of any of the gas power boats that had problems just diesels. I have a new set of Bravo III drives that are powered by 5. 0 gas engines at 260 HP. I am going to put it in the water next week and I hope that they work out. The new gas set up for twins cost $25K. Any way good luck with your project.