Joan & Jackie
A funny and informative interview with Marilyn "Jackie" Horne and Joan Sutherland from Life Magazine '70 can be read here—A Tour of Two Great Throats.
You'll want to scroll a few pages up to the read it from the beginning. I stumbled upon this article in the process of looking for more information on Sutherland's mother. The NYTimes obit stated that she studied with Mathilde Marchesi, which seemed a bit of a stretch.
And indeed it is. After a trip to the library when no online sources were forthcoming, I learned that Sutherland's mother studied with Burns Walker, a student of Nellie Melba (Singers of Australia by Barbara & Findlay Mackenzie, 1967). It was Melba who had studied with Mathilde Marchesi.
But back to the Life article. Sutherland and Horne sound like two pals chumming and hamming it up for the interviewer; making comments about weight, the trials of being onstage, audiences, and all manner of things including vocal technique.
If you know where to look, you can find just about anything.