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It was the late 750's and maybe the 550 K3(not sure) that did not have the flats. All early 750 and 500 did have
Far as I remember its one of the few times the part number did not change, nor the picture in the parts book, the only one that needs the flats is the early 750 that has the drive plate locating on them and the chrome trim with no indentations for the later drive, or if you want to fit twin discs easier!