According to the National Population and Housing Census 2011 the overall Dura population numbers 5'394, a slight upturn from the 5'169 recorded in the 2001 census. Note that overseas resident are not counted. There is a sizeable number of Duras in Britain. I would be interested to know where you found the number 2'160 as in your entry on Dura.
I have been working on the surviving data on the language and suggest that the classification as West-Bodish is obsolete. Such a genetic unit has never been demonstarted as a valid subgroup. Rather, I suggest to classify Dura under a Greater-Magaric or West Central Himalayish group as Dura appears to be more closely related to Magaric and Bhujel-Chepang than to either Tibetic or Tamangic (Schorer in press).
A field trip to Nepal in 2015 has shown that Tandrange is indeed intimately related to Dura. In fact, much of the lexical data collected by local scholars and language enthusiasts such as Kesh Bahadur Dura were actually gathered in the Tandrange area. For socio-political and economic reasons, the population of those villages had taken on the ethnic guise of Gurung. As of 2015, the Tandrange people do not entertain any queries on part of the Duras regarding language documentation or a closer collaboration.
Department of Linguistics
University of Bern, Switzerland