The Chumharigang is located (28° 2'47.93"N 90°27'17.27"E) at Bhutan-China border about 6 kilometres west of Gangkhar Puensum.
The mountain shown on the 1984 souvenirsheet looks very identic with Chumharigang seen from the west. It seems to be a view from above the settlements Lonzo and Thanza (appr. 8° 4'42.23"N 90°10'36.56"E).
A similar photograph can be found on fickr fotostream of steynard (link).
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The photograph shows Chumharigang (foreground/middle) and the Gangkhar Puensum (behind/right).