The Allied boat company built some solid boats: Sailboats built by Allied Boat Company Inc. on Sailboatdata.com
The Greenwich has a 3' draft which should be perfect for the Great South Bay: GREENWICH 24 Sailboat details on sailboatdata.com
The ocean inlets to the GSB can be treacherous though so you really will want to have confidence in your OB motor and time your passages with the tides.
On boats of this era you will want to check the integrity of the chain plates and check the decks for any soft spots. Also check rudder bearings/gudgeons.
My T27 is from 1967.
I sailed on a MacGregor 26 S from Babylon, out Fire Island Inlet to NYC and eventually Yonkers.