As abordagens de ILS eram de uso comum em 1970, quando recebi a classificação do instrumento. O teto normal (Cat I) mínimo era de 200 pés. Então, sim, um 707 teria sido capaz de pousar com um teto de nuvens de 300 pés nos anos 70.
Eu verifiquei Wikipedia e encontrei o parágrafo de histórico abaixo:
Tests of the ILS system began in 1929 in the United States.[14] A basic system, fully operative, was introduced in 1932 at at Berlin-Tempelhof Central Airport (Germany) named LFF or "Lorenz beam" due its inventor, the C. Lorenz AG company. The Civil Aeronautics Administration (CAA) authorized installation of the system in 1941 at six locations. The first landing of a scheduled U.S. passenger airliner using ILS was on January 26, 1938, when a Pennsylvania Central Airlines Boeing 247D flew from Washington, D.C., to Pittsburgh, Pennsylvania, and landed in a snowstorm using only the Instrument Landing System.[15] The first fully automatic landing using ILS occurred in March 1964 at Bedford Airport in UK.[16]
A CAA mencionada na citação foi a precursora da FAA dos EUA.