You would need a tensioner if you go with a double. The bar ends will not work. Well, you could put them in friction mode, but that is not ideal. You might just barely shift or just a bit too much shift and the gearing wouldn't be how it is suppose to be. JTEK Engineering does make a bar end for the 7 speed. You could also use the Shimano shifter with a plug that goes into the end of your bars. I forget what it is called.