there are actually a few drop in HID projectors conversion kits for our S13 flip headlights
http://www.brightheadlights-hid.com/hid-upcoming.htm
im currently using Hella H4 conversion kit though but the cut off line is sharp. im definitely gonna try to put some HID in them.
you can check out the cut off line here
http://www.zilvia.net/f/showthread.php?t=152196&page=6