A. Not likely they could target a specific part of the ship. The mussiles are radar-homing, so the center of the radar return was the target.
B. The Moskva was an old ship, so pretty much everyone knew plenty about it, even in the west. I remember an article on it in the Naval Institute “Proceedings”, the USN trade journal, back when the Moskva (then the Slava) was new, and I dont recall that it got much wrong, even 40 years ago. Its perfectly possible to tell where the magazines are just by looking at the ship. Actually, that also goes for most warships.
Much appreciated! You know more than I do.