| Problem with drilling in situ is because the nut's not clamped it's likely that the bit will bite the head of the nut and just spin it instead.
Then all hell breaks loose as the drill spins off across the bodywork / casings etc
It's got to be worth the aggravation of dismantling just for the piece of mind.
I'd offer the use of my bench drill, but I'm miles away from you | 
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