Re: The layers keep piling up
"Unbolt rocker shaft ... Refit rocker shaft ..."
At the risk of seeming petty, that sounds like Central (Single Port) Fuel Injection where a single fuel injector replaces the carburetor. I'm told that nowadays most cars use multiport injectors -- one for each cylinder. On my last three cars, the fuel injectors are mounted on a fuel rail running down the engine above the intake manifold and are activated electronically. No need to remove the valve(rocker) cover to change them, They are as accessible as they are going to get from the top of the engine. They look to be easily be replaced by any abnormally flexible individual with small hands and three or more functioning arms. Caveat. I haven't had to mess with a fuel delivery system since my 1969 Mazda carburetor automatic choke died of old age about three decades ago. I'll be overjoyed if it stays that way.