On a slightly more serious note :lol: - I think the gearbox will physically fit ok - but you may find that they have different clutch release bearings/arms etc - so you may need a newer type clutch pressure plate (or possibly convert it to earlier style - but not sure if thats possible).
Just checked the bible - it reckons the cluch release bearing was changed start of 71, however the gearbox mounting wasnt changed til 72 - so I guess if that doesnt get in the way you should be good to go.