All now in (literally on the back of an envelope, noting the 'grid references' on the online version against the solutions. I'm still not completely convinced that I've got the right fit of the two possibilities though, as I still haven't found a second indication in the clues. It could be C.
Hi MacGee - like you I have finished it but I don't see the significance of the instruction. What a belter though! Probably have been quicker if I'd printed it off - took nearly an hour.