Hi Ray,
I was also wondering whether Rueben P. with the daughter Betsy was 'our man'. Her age and his occupation match. And Rueben did not sign his own name on the census return.
I would speculate that Portner was an Anglicisation of the Russian surname PORTNOY, which means tailor in Russian (= kravitz in Polish) and was documented in many places throughout the Jewish Pale of Settlement including Vilnius.
Justin