Like always there was some research done before the first prototype and then it went to the build phase and the prototype was made
After the first version the second was made, fitting more to the size and shape of the real Skylab
This also featured the telescope module of the real Skylab, and that was Skylab built. But there was one problem, how do you bring the telescope on the side?
The solution was to launch the telescope on top then relocate it once in orbit, all that was left was to integrate it to the Saturn V
The Skylab was mounted to a Saturn V without the third stage, and it was ready for launch. As always here are the comparisons