Which one for the lower unit drive shaft? Would it matter? Seems like the pulley would be best?

Well sprocket your talkin chain which wouldn't give much if your hitting hard objects... pulley will have some forgiveness when you do strike something hard... We've used the gt2 (I think) by gates and it has worked flawlessly, but I have heard of others on here particularly Mark C. who uses a different setup that should work and is less expensive? I'm sure he'll chime in! good luck!