This Aerojet-General report from 1964 discusses the possible future evolution of liquid oxygen / liquid hydrogen -fueled rocket engines from 1966 to 1986. From the M-1 rocket engine to the notional Advanced Engine, Ducted Rocket, and then Advanced Air Cycle for post Saturn launch vehicle applications such as Nova.
Advanced Engine Systems by RC Stiff, Aerojet-General Corporation
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19720062794_1972062794.pdf
Advanced Engine Systems by RC Stiff, Aerojet-General Corporation
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19720062794_1972062794.pdf
