If this is one of the £24.99 jobbies from eBay then I also had issues fitting to my 600 2001 box eye fazer, it was just too tight to line up with the side plate holes, and yes I removed the side plates.
In the end I had to file out the holes on the guard to make them wider and then it just about fitted, but I was never really happy with it as it bowed out slightly, it seemed the bend in each side of the guard was not quite in the right place.
Many years ago I had a Beowulf guard fitted to a 2000 600 box eye and it fitted beautifully with no issues, I don't know whether it is the guard at fault or a change in the radiator fitted to different years, I had my suspicions it was the guard.
Just my tuppence worth