Fuel injector rebuild kits are designed to help you service and maintain the fuel injectors in your engine. These kits typically include a variety of parts such as seals, filters, O-rings, and more that can be used to replace worn or damaged components in a fuel injector.
The specific models you've listed:
are all large, powerful engines typically found in marine applications, like boats. The numbers 454 and 502 refer to the engine's displacement in cubic inches.
Please ensure you have the correct rebuild kit for your specific engine model to ensure compatibility. It's also important to follow all manufacturer instructions when performing maintenance on fuel injectors to ensure safe and effective operation. If you're not confident in performing this kind of maintenance, it may be best to seek help from a professional mechanic.