If you're looking at a site/company that has HIDs for motorcycle offerings, double then. You will need two burners, ballasts and igniters, one per side.
HIDs do not have dual filaments like their Halogen counterparts. The 4th gen does not use a dual filament setup either. HIDs accomplish highbeam and lowbeam on with one HID burner per side by having a movable sheild in OEM setups, i.e. Bi-Xenon.
If possible post a link of vendor you're looking at and I can tell you if the kit has everything for you to complete the setup.