01 ZX6R ENGINE SWAP

[Jaffa58]

I have a 01 ZX6R and the K's are getting high and am thinking of slipping in a 636 motor if I can find a lower K motor. Is there much difference in the original 599 and the first 636 in how it fits? I've had little to nothing to do with the ZX6R before so any info is good info...thanks