@seeker, yes high caste newars(joshis,rajopadhyas,pradhan etc) are more hinduised since they are ethnically mixed with lichhivis and mallas and have been hinduised longer than the khas people.newar were hinduised since the 5th century AD or so, whereas the first manuscripts of khas from 12th century show they were still buddhist and shamanist(masto worshippers).
i also believe upadhyayas have non-khas origin as i mentioned earlier.these north indian brahmins brought the more orthodox brahmanical hinduism to our hills and hinuised the khas and magar in western hills.
@nas,vedas were pre -hindu documents of aryans . upanishads were the intepretation but these scripts were not originally written/read by native nepalis.even the valley kings who were the first hindus of nepali hills revered tantric,shaivaite and shakta religious books more than brahmanical books.i am not saying vedas and upanishads being only brahmans book, vedas were documented a lot later by brahmins though the source is basically social wisdom ,prayers and migration story. upanishads are a later creation from mostly north west indian brahmins.they are the property of whole humanity but are not innately nepali.