If it's not going to be winter-driven, then the LSD is only of limited value. Really, if it's that nicely restored, are you sure you want to drive it on salty, slushy roads in the first place? My 'vert is in good shape but is by no means a well-restored specimen, so I have no qualms about driving it in winter.
Plus, if you're going to winter-drive it, consider finding a hardtop.
By the way, the small metal tag is, IIRC, visible if you scoot under the car from behind. Years of wear may have damaged the tag, so you may have to get close up to see if there's an "S" on it, but it should be relatively easy to find.
<img src='http://www.tinsmithtech.com/graphics/sigpic.JPG' border='0' alt='user posted image' />
Dad's 1992 325iC