Working on the big Cat was cool because of the size of it. The thing I learned most by working on this engine was how the fuel injection system worked. This engine has an all mechanical fuel injection system.
The rocker arm in the middle is for pushing down the injector plunger. The fuel is piped through fuel lines that connected to the cylinder head. You can see the pipe fittings on on the neighboring cylinder heads, between the cylinder head bolts. Below the top end of the rocker arm is the injector and below the bottom end is the push rod.
Here is the big injector all apart
Looking straight down into the part show in the above picture, you can a rack and pinon. As the piece that is sticking out of the side of the top part of the injector, is pushed back and forth, it will turn the plunger. Thus this will adjust to amount of fuel injected into the combustion camber.