I've never installed one, but there's only one way forward: you need to enlarge the chassis hole to 10 mm. I can think of a few ways of doing this: (1) drill in small increments - starting with a bit just barely larger than the existing hole - you need pointed bits so that the bit self-centers (no spades); (2) round file; or (3) a hand deburring/scraping tool - the kind that has a sickle shaped blade. The latter is a surprisingly effective method for making modest hole enlargements in aluminum.
cheers, Derek