im getting the black housing headlights for my is300...is it true that the stock HID's wont fit the new lights?..if so then what size HIDs would i need?

 

If you're just getting new housings that are HID as well then the stock bulbs will fit in no problem. All HID housings thats use reflector bowls have D2R bulbs. As long as the other set you're getting is HID as well then you will have no problem fitting your current bulbs.

 

all is300 housing are hid, so they are all the same