The Mark IIA project involved modifications to the telescope to increase dish size to 100 ft as part of the multi-telescope interferometer network. It would have made the Mark II the largest telescope in the world operating at wavelengths shorter than 10mm (proposed down to 6mm) . The project was cancelled by the SRC in 1975. The bowl of the Mark II was upgraded in 1987.
The file includes correspondence with the ARC, UKAEA, the Royal Observatory, Edinburgh, the national Radio Astronomy Observatory and H C Husband. There is a significant correspondence with the latter relating to initial concerns over reflector accuracy and continuing to detailed discussions of the alterations required.