Flex plate is the recommended way to go. Just don't go to your local salvage or dealer and buy a regular car flex plate. Like said above they can Flex without the converter bolted to them. This usually results in starter problems sooner or later. Buy a good SFI or the thicker flexplate that is used in the patrol cars. A lot of people don't realize that a starter works harder in a jet boat than it does a car because it not only has to start the engine, it has to turn the pump shaft, the drive line, loaded impeller and move water all at the same time. Running a flex plate in a jet boat is not harder on the engine than the flywheel because the pump shaft, drive line, and impeller serve as the flywheel. Just use a GOOD flex plate. Pioneer makes a good thick one at a reasonable price for most applications.