n0mesorah,
3) Rav Moshe is not sure if mechitzos would help for Brooklyn. It is mefurush in this teshuva. He never mentions that there aren’t mechitzos. In the other Flatbush teshuva it only mentions dalsos and reshus harrabim. So, clearly there was some consensus that mechitzos were not enough.
(או”ח ה’ כ”ח או”ק ה’) וז”ל: ומצד מחיצות סביב ברוקלין כפי
הידיעה שעד עתה אינו כן וזהו אפשר לברר עכ”ל.
There is no doubt that Rav Moshe would not have a problem if do not include the bridges that mechitzos are sufficient for Brooklyn.