In order to carry the state, the GOP candidate must win 55-60% on the Island, 2/3 upstate and garnish at least 1/3 in the boroughs. It's really tough to do. Democrats outnumber Republicans 46-27% here.
Reagan won almost 2/3 of the island, 2/3 upstate and 1/3 of the boroughs and still only won by 8 pts in 84.
Long Island was once very Republican. It isn't anymore. Going back to the time you are talking about, Republicans controlled everything on LI. No we have both legislatures in Dem hands, both county execs in Dem hands, both DA's in Dem hands, 4 of the 5 Congressman from LI are Dems. The area isn't GOP anymore. This isn't the 80's anymore....
In fact the Dem shifts on Long Island along with Westchester is the main reason why LI has changed from lean Dem to strong Dem.