Don't know if it'll work since I don't know what it's ends look like or if there are other clearance issues due to diameter or reservior location, but the GSXR1000's shock comes in different lengths depending on year and none of them are the same as either the 1G or 2G B12.
Eye-to-Eye lengths:
1G B12 306mm
2G B12 320mm
01-02 GSXR1000 329mm
03-04 GSXR1000 332.5mm
05 GSXR1000 325.5mm
That said, it's well known the '99-up Hayabusa shock at 330mm will fit the 2G B12 without much trouble, but will alter ride height.