Oops, I have an old Cannondale with 7-speed Shimano DT shifters and should have recognized the picture. But It's been at 20 years since I set it up. I believe the Shimano's DT shifters from back then came with the extra flat covers needed for a Cannondale. But it doesn't look like the current SL-R400 comes with anything but the concave mount for round steel tubes. Finding a used set with the flat covers might be a slim chance but used 8-speed bar ends should be easier to find as they were common on touring bikes before 9 speed was trusted travel down the long roads.