Best I could do with the images I have: (sorry I couldn't make it any bigger) again the scanned quality isn't great!
Bit hard to describe, but the lip slots into bumper. Just under that there is a raised edge which is held in place by plate(s), that have a 10mm bolt(s) holding them in place.
You could probably get away with cable ties or self tapping screws.
Self tappers would be a lot easier, or cable ties if your lazy!
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