I'm sorry about the poor quality of these images. They were copied back when the black & white copy machine was the only choice. That is except for the concept drawing with the visible tankage - that one was a frame grab from one of the NASM Laser Disks.
The following are excerpts from "An Integrated Space Program for the Next Generation" printed in Astronautics & Aeronautics, January 1970. This twenty-two page article has information on various components of that great 70s space program that wasn't.
The space tug, another reusable space vehicle in this strategy, would be designed for operation in the space environment only. Initial thinking calls for a propulsion module weighing about 50,000 lb with a fuel load of liquid hydrogen and liquid oxygen. The module would be about 22 ft in diameter and 25 ft long. The tug would employ an attachable module with living quarters for three to six men. For some applications, this crew module might have external manipulator arms to aid assembly and repair operations. (Page 38)
The tug would normally be docked at the space station, and the space shuttle would refuel and resupply it. (Page 38)
The tug itself would be carried into orbit by a Saturn-V. Initial design studies indicate that one Saturn-V launch will be able to deliver one space station module and several space tugs into low Earth orbit. (page 38) (Mike Burke's note - I think this launch scheme was only one of the concepts studied.)
The space tug (gross weight 80,000 lb) will be adapter for lunar landings by adding landing gear like the LM descent stage's. Deployed from the space station in lunar polar orbit, it will be able deliver substantial payloads on both legs of a round trip to the moon's surface. For example, if it carried 27,000 lb of cargo and passengers to the surface, it could return 7,000 lb to lunar orbit. (Page 44)
I hope you find this information useful. I have prepared a set of drawings for building a 1/96 scale model Space Tug. I think I should post those in another category on the forum.