This is what l done.
First l had to cut off the rear sump guard mount so the engine would sit right.
The spindle that goes through the swinging arm and engine is bigger for the 450 so l had to get a sleeve made up, didn't cost much.
The bottom engine engine mounts need to be moved forward or what l did was file out the bolt holes and use a smaller engine bolt.
The top engine mount on the 400 has 3 bolts through the frame where the 450 only has 2, you'll have to use the 450 brackets and cut off the front bolt hole from the frame, l was going to just leave it unused but found because the 450 has the coil built into the spark plug cap there's not enough room to get the cap on and off other wise.
l've fitted a battery in the airbox strapped to the lid and drilled some holes in the airbox because the battery takes up a lot of room.