I picked up a set of 1IS3 rotors last summer for my GS and put them on, no issues with fitment. Just for giggles, I was looking at car-part.com and it shows the 1IS and 2GS have different rotors.

What is the diff?

 

Centric lists it as the same part #

 

front or rear?

 

I have IS300 rotors in all 4 corners right now, I couldn't visually tell a diff. supposedly the ones I have are OEM rotors (came from a low mileage car he put on slotted/drilled, then sold car)

My guess is the differences are minimal.