Now updated to fit perfectly without any gap between the mirror and the adapter. Current Photos besides the first one are the V1 version. Photos will be updated shortly.
These Adapters will allow you to use GKTech Aero Mirrors or Aliexpress Fake Ganador Mirrors on your IS300. They fit perfectly inside the OEM mirror rubber boot and you can reuse the original hardware. To attach the mirrors simply use the silver hardware the mirrors come with.
 
These are the mirrors that will fit and must be purchased separately.
Purchase Mirrors Here or Here From Aliexpress