The floorplans of McCormick can be accessed here:
https://floorplans.mit.edu/ListPDF.Asp?Bldg=W4
McCormick is composed of two towers, the East Tower is rooms ending in 21-40 and the West 0-17. Rooms 45, 55, 75, 85, and 95 are in the Annex (a brownstone house attached to the east side of McCormick.) The Annex is W-2 and the floor plans are here: