Thanks to a friend who pointed me to this information.

Here is an oral history from the residents of Conantum, a neighborhood of Techbuilts designed by Carl Koch.

And here is an in-depth 1992 interview with Carl Koch. All of these interviews were conducted by Renee Garrelick. From the site:

The Renee Garrelick Oral History Program (also known as the Concord Oral History Program) consists of interviews with Concord citizens from all walks of life. Begun in the 1970s, the program has resulted in the collected histories of hundreds of Concord citizens. Iinterviews through 2006 were conducted by Renee Garrelick and transcribed by Nancy McKinney. Photographer Alice Moulton’s portraits also form an important part of the collection through 2006. Renee Garrelick died in January 2007. Since 2008, Concord Oral History Program interviews have been mananaged by the Concord Free Public Library and conducted by an outside contractor.