'In the predominantly Jewish neighbourhood in which I grew up, most immigrants described themselves as not simply as "Jews", but as "Polish Jews", "Russian Jews", "Romanian Jews" "Litvaks" (ie. Baltic Jews) etc., in the same way Irish immigrants identified themselves as "Irish Catholics".'
I am not sure what country your neighbourhood was in (America, Canada?) but I can see that your Jewish neighbours did not identify themselves as American Jews (or Canadian Jews). Might their Polishness or Russianness have been a post-immigrant identification? Would they have identified themselves as Polish Jews in Poland, or Russian Jews in Russia? I don't think that was typical. You might say that it would have been redundant, but I think the point is that it just was not true, not as anyone, Jew or gentile, saw it. Germany is a bit different, with its long tradition of acceptance (before that was all turned on its head, of course). It is on migrating that the different Jewish communities felt ties of national origin to be valuable - shared language and experiences.
'I don't recall the Jews being any more conscious of belonging to a "chosen people" than any other religious or national group which invariably flatters itself as possessing unique virtues.' Well, benighted people might have been more accurate, but plainly Jewish, I think was the bond that tied them together.
You say
'A large minority of left-wing Jews, in fact, insistently saw themselves as workers first and Jews second, and generally viewed ethnic affiliations as parochial and reactionary.' Yes, that is true. Certainly it was in East London, where many Jews settled.
I once went to a talk by Teodor Shanin where he went into the question of ethnic identity in the USSR. His passport, he noted, bore a stamp 'J' for Jew against 'nationality'. He did not think that in itself represented persecution, as he said, in the USSR everyone had a 'nationality', what we would call an ethnic identification, underneath their citizenship of the USSR, like Russians, Kazakhs ... and Jews. We asked him about the ideal of living without nationality. He said yes, you could see that there was a point in the 1920s when bolsheviks had tried to live the ideal of internationalism, to have no nationality, but that it had not survived the 1930s.