Preliminary details of the 7-7 were revealed at The '81 Paris Air Show. The plans were for a twin engined 150 seat short/medium range jetliner with a larger fuselage cross section than the 737. As much commonality as possible would be sought with the 757 components, such as the flight deck, front fuselage, rear fuselage, tail unit and many of the systems. The wing and engine installation would be new, together with the undercarriage.
At that time Boeing indicated that the earliest in-service date was likely to be 1988 as the company was occupied with the 757, 767, 733 projects. Boeing was planning to optimize the design to achieve the lowest fuel burn over ranges of 500nm/925km, while the design range would be 1500nm/2776km and the design speed would be Mach 0,75 - 0,78.
Source: An Illustrated Guide to the World's Airliners by William Green Gordon Swanborough, 1982.
. The book also features the rendering with the plane in silver/gold/brown/black livery, but I don't have the possibility to scan it.