What are the dimensions of that new disk? EDIT: See below.
I know for a fact the same disk is not used on all 550's they list.
and some of their year and model designations are not correct.
I found this page which seems to show other disks available with a better breakdown of what model should get which disk:
sydfynsmcservice.dk/kawasaki/kawasakibrskvrustfrifor.htm
That chart seems to be showing the European versions of those models (not surprisingly) which may have come with dual front disks. The U.S. sometimes got single-disk versions of the exact same model.
I think it shows the 077004 DRF-409 is 260 x 130 x 5.
This would be correct for the 81 Kz550D1 which is dual front. (Rear is 7mm thick.)