One of the earliest designs for a “wet lab” space station based on the S-IVb stage that can be directly traced to Skylab ancestry. This piece of NASA-MSFC artwork dates from 1966 and shows clear similarity to Skylab. The Apollo telescope mount is still clearly derived from the Lunar Module; the solar panel arrangement is obviously quite different, and it has retained the aerodynamic shrouds (which were probably meant to serve as micrometeoroid shielding). Another telescope is shown directly opposite the Apollo mount, and there’s of course the J-2 engine way at the back.
Drawings to come.