I don't know if I will work perfectly, but I suspect it will work. When I have encountered real world qureries about cross compatibility, generally the answer is "TRY IT". That's what a respected mechanic at a local bikeshop has told me. I still use 6 speed and I'm in the same position of gradually moving to 7 speed. I know I'm way behind the time but all three of my road bikes have 126mm rear triangles. I don't think the spacing is any different between Shimano 6 speed cassettes and freewheels compared to the 7 speed cassettes and freewheels. So the derailleur pull should be the same. Try It and post back here your real world empirical result...O.K.?