hello mate, before you try the allen key, with a heavy hammer and drift the same size as the nut, try hitting the nut face on, this will free off the rust that is between the threads. also spray with WD40, dont use a allen key ,you need to buy a allen key bit that fits into a socket, and a good size half inch drive breaker bar, try the bigger allen key, if no luck than you will need some heat on the nuts to free them off first. hope this will help you.
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so the moral of the story is aim your ass at the nuts & fart[][]