Three American examples come quickly to mind.

The first is R. Buckminster Fuller, perhaps best known today for his development of the geodesic dome. The DIY dome was popular - for a while - as a counterculture structure in the 1960s and 1970s. In addition to the dome, Fuller’s other writings about technology and culture were also popular; his writings appeared in the Whole Earth Catalog, for instance, and some examples can be seen here. His lectures were also well-attended, and you can find some of them, along with other media appearances, on YouTube.

The second is Scott Nearing, who may be less well-known. Nearing had a lengthy life as a pacifist, advocate, educator, writer, and activist. One of the ways in which he gained attention and influence was as an advocate of simpler living. Most particularly, his advocacy of “back to the land” and “homesteading” are often seen as inspiring parts of the counterculture movement in the 1960s and into the 1970s and beyond. Along with his second wife, Helen, in 1954 he co-authored Living the Good Life: How to Live Simply and Sanely in a Troubled World, which described their experiment in going “back to the land”. They wrote extensively on this and related subjects, well into the 1970s.

The third, Marcellus Jacobs, was born in 1903, and so might not strictly speaking meet your criteria. He also doesn’t seem to have acquired prominence until the early 1970s. I’ll mention him anyway, though, since he will likely be of interest, and by the time he gained counterculture attention he was in his late 60s or early 70s. Marcellus and Joseph Jacobs founded the Jacobs Wind Electric company in the 1920s, and built their business on providing wind generating plants for remote areas, including rural areas before rural electrification programs. The company stopped manufacturing its original designs in the 1950s, largely because of rural electrification. The energy crisis of the early 1970s led to a renewed interest in wind power, both by governments and private individuals, and Jacobs was involved in this rebirth. Jacobs’ experience and knowledge were sought after by government and by others, such as in this 1973 interview in Mother Earth News. Original Jacobs equipment was sought out for restoration and re-use because of its quality, durability, and ability to be rebuilt. Even into the 1980s, articles about wind power generation would recommend locating and reconditioning old Jacobs equipment, even in preference to some newer designs and manufacturers.