Mick,
I would say that the right hand pipe is not for an MC21, or you have an aftermarket rear shock with added ride hieght.
You can do a couple things.
1. If it's a pipe for an MC28, get one for an MC21.
2. If you have added ride height, you can create a small spacer for the mount that moved the pipe down a little to clear the swing arm.
Thanks
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Charles Gallant