While building this F1 engine tested my abilities with CAD, I actually learned a lot about how this Closed Gas Generator Cycle engine works. After spending several weeks on it, I now know how the entire system works together from the fuel inlets, to the main fuel and LOX valves, the turbpump, and even the exhaust manifold.
Building Stage was definitely more simple than designing the F1 engine as it is just a long body with a fuel container and LOX container. But adding otehr details like the forward and aft skirts as well as the plumbing lines made this a lot more interesting.
Building the J-2 Engine also gave me some great insights into how this gas-generator cycle engine works. There were many similarities between the J-2 Engine and F-1 engine with the exception of there actually being flight instrumentation on the rocket engine itself which I found to be quite interesting.
Stage II was also fairly simple, but more complex than Stage I. On the outside you can see a control panel which contained additional flight instrumentation. Below stage II is the first interstage which connects it to the first stage, and above stage II is the second interstage which connects it to the third stage.
Stage III used the same J-2 engine as were on Stage II and was really similar to Stage II with the exception of being significantly smaller and only having 1 engine versus 5.
And here is the entire rocket put together!