Genuine S laygear- all pre-rod change 4 synchro gears were the same except for the laygear and 1st motion shaft-The Cooper S and 1275GT had a closer rato with a 18 teeth 1st motion and 29 teeth (15,20,25,29) 22G1040 laygear.
One of the most sought after 4 synchro remote box close ratio gears. The most certain identification is done be inspecting the laygear.
If it is a 22G1040 laygear you have a close ratio box. While you are inspecting the laygear be sure to check the inner surface of the laygear which serves as the outer race of the layshaft bearings. This surface can breakdown resulting in premature failure of both the bearing and the shaft.
Ist motion shaft to go with this has 18teeth--22G1371 14mm nose mainshaft or DAM3167with later type 18mm nose mainshaft.