if metal, rivets would be least obvious fixings as far as cosmetic appearance goes.
tek screws as has been said is a good option but remove the washers on the tek so they are less bulky looking.
there is always VHB tape or similar, but you’re getting one chance to get it right before its stuck.
I would probably consider partially bonding it with tigerseal if it doesn’t need to be removed in the future, this will allow for a lot less visible fixings if any at all
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