I believe that the postage stamps depict the Marshall Spaceflight Center and McDonnell Douglas 12-man space station. Artwork and description from
NASA Images.
This picture illustrates a concept of a 33-Foot-Diameter Space Station Leading to a Space Base. In-house work of the Marshall Space Flight Center, as well as a Phase B contract with the McDornel Douglas Astronautics Company, resulted in a preliminary design for a space station in 1969 and l970. The Marshall-McDonnel Douglas approach envisioned the use of two common modules as the core configuration of a 12-man space station. Each common module was 33 feet in diameter and 40 feet in length and provided the building blocks, not only for the space station, but also for a 50-man space base. Coupled together, the two modules would form a four-deck facility: two decks for laboratories and two decks for operations and living quarters. Zero-gravity would be the normal mode of operation, although the station would have an artificial gravity capability. This general-purpose orbital facility was to provide wide-ranging research capabilities. The design of the facility was driven by the need to accommodate a broad spectrum of activities in support of astronomy, astrophysics, aerospace medicine, biology, materials processing, space physics, and space manufacturing. To serve the needs of Earth observations, the station was to be placed in a 242-nautical-mile orbit at a 55-degree inclination. An Intermediate-21 vehicle (comprised of Saturn S-IC and S-II stages) would have launched the station in 1977.
http://www.nasaimages.org/luna/servlet/detail/nasaNAS~9~9~61574~165421:?qvq=q:space+station+concept;lc:nasaNAS~20~20,NVA2~14~14,nasaNAS~4~4,nasaNAS~5~5,NVA2~8~8,NVA2~16~16,nasaNAS~22~22,nasaNAS~13~13,NVA2~20~20,NVA2~25~25,nasaNAS~6~6,NVA2~1~1,NVA2~9~9,NVA2~27~27,NVA2~18~18,NVA2~22~22,NVA2~13~13,nasaNAS~10~10,nasaNAS~7~7,nasaNAS~8~8,nasaNAS~12~12,NVA2~24~24,NVA2~15~15,NVA2~4~4,nasaNAS~9~9,NSVS~3~3,nasaNAS~2~2,NVA2~17~17,NVA2~21~21,NVA2~26~26,NVA2~23~23,nasaNAS~16~16,NVA2~19~19,NVA2~30~30,NVA2~29~29,NVA
2~28~28&mi=32&trs=318
I believe that is also known as the S-IVB Advanced Station.
Follow-on to Skylab proposed by Douglas. The station would still use the S-IVB stage as the basis, but would be much more extensively outfitted for larger crews.
Artwork appeared in
Frontiers of Space by Philip Bono and Kenneth Gatland
http://www.astronautix.com/craft/sivation.htm