It is quite correct that Richard Avedon and Irving Penn (not to mention David Bailey and many others) have exploited the "distortion" of a standard lens used close up to take portraits. In fact, even a 120 or 150 mm lens still has some "distortion" but not as much and gives what is usually regarded as conventionally pleasing result (the only downside is that it does make people look a bit fatter than they really are, so care is needed with subjects with a tendency to largesse).
Strictly speaking, a lens of three times the "standard" focal length or more (250 mm or more with 6x6 cm film) gives correct perspective, but in practice the results can look a little flat and lifeless. Whenever possible, I like to take portraits on my Keith twin-lens 4x5" camera, this has 10-inch lenses, roughly the equivalent of 150 mm on 6x6 cm.
Regards,
David