There's no single "Point gap" for a 1975 Ford 6-cylinder. The correct point gap depends on the *specific* engine model. Ford used several different inline-six engines in 1975 (e.g., 170 cubic inch, 200 cubic inch, 250 cubic inch). Each engine had a different recommended point gap.
To find the correct point gap, you must consult your owner's manual or a Ford repair manual specific to your engine's displacement (e.g., 170, 200, or 250 CID). These manuals will provide the precise specification.