Your limited by the mechanical pump. They have a 4 plunger pump out there that flows some fuel. Compression will need to be lowered and studs. New heads that are the hd heads, thicker. Good free flowing exhaust. Intercooler and possibly **** injection. A good none restricted turbo, not a 7.3 turbo. Marine injectors are a gimmick unless they are set to the high pop pressure but most aren't. They do have a custom cam out there for a 6.5. You don't need a custom crank, maybe a scat crank but what you do need is a fluid damper. I can go on and on but will stop here. You can get 300hp look at Peninsular Diesel they sell a 300hp marine 6.5.