Saratoga's 1936-1940 pre-war island is a bit different in deck shape and details (uppermost level, splintershielding and fighting top are different) and those differences may or may not matter to you.
If the deck shape and other details do matter, and you'd like to build your Lexington model using the Lexington kit's as-is hull and flight deck, a 3D-printed Lexington 1936-1940 island is available: http://shpws.me/NfRK
Other 3D-printed 1/700 scale islands and funnels are available representing other configurations of both ships. Links are at the bottom of the Lex island page.
Best wishes on your build!