that is only one battle in a war of sorts you will have to get the 450 wiring harness figure out how to mount the fuel pump not to mention the cost of a 450 engine if it was me id just big bore the motor or sleeve it i have a 2004 kfx400 with a wiseco 453 sleeve kit 13.5-1 piston and some old profile hot cams more lift and duration then the cams they sell now i plan to get some porting done on the head still havent spent the average cost of you engine swap will run ya anyways good luck post more info as soon as you can
I think if you could find the motor with every thing to run it cheap enough, then yes, if you want some thing unique. If you just want a 450 you could always just sell the 400 and buy a 450. It all depends an what your going for and how you ride. I will actually be putting a kfx 450 motor in a tecate here soon but it is going to be a chore and take a while bit I like to build bikes that have not been built yet, and I currently have a tecate powered by a crf 450 motor. Any thing is possible man. Would you be doing the work your self?
i would be helping with the work but i know a guy who does this kinda stuff everyday so he would be doing most of it. i just want the 450r motor for the fuel injection. but i am not sure if its worth it