Do you have a Hellcat engine being used for mockup until you get to the fuel system?
You should cap all of the holes/cavities exposed. Especially the fuel rail, where contaminates can enter and potentially clog your injectors.
We see engines all the time fully exposed in a dirty shop; weld splatter, grinding dust, etc can harm your engine and not even know it.
This fuel rail cap is one step in protecting your engine during that time.