It is a different nozzle. Many people have put 603 nozzles in 617s and it's worked fine. Actually better because the 603's nozzle is a little different to provide a smoother idle.

But this guy's wanting to go the opposite way 617's into a 603. I think it'll work.

As far as the physical difference, GSXR here on this forum (Dave from Idaho) has a MB Factory Manual picture somewhere posted of the difference and and explanation/reason they used the nozzle they did vs the old 61x nozzles.

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