Via the Asian Studies WWW Monitor, this set of 1940s Tibet photos taken by an American army expedition sent to Tibet from India to see about getting supplies to the KMT.  The collection of over 200 black and white photos is maintained by Dr Rob Linrothe, Associate Professor and Director of Art History at Skidmore College.  A few were published in the early 1980s but many remain unidentified.

This photograph by Tolstoy is published in Tibet: The Sacred Realm (p. 101) where it is captioned: Dancers in Cham dance, 1943." It also appears in Tolstoy's National Geographic article, where the caption mentions that it was taken at Gyantse. Presumably, the other photgraphs of masked and unmasked dancers were also taken at Gyantse.