From the Ric website "Basically the same as Model 330 but with twelve strings. Careful acoustic research has resulted in the full, rich and warm sound of this popular model. Two single coil pickups on a full size body are accented by a traditionally shaped sound hole. The 24 fret Rosewood fingerboard is punctuated by dot inlay fret markers, with full double cutaways permitting access to all the frets." http://www.rickenbacker.com/model.asp?model=330/12more
The Rickenbacker 330/12 is a near-classic, the reason being that the 360-12 is much more seen in the hands of mighty stars than the 330/12. Now I will write about those subtleties that people tend to overlook in favour of telling you how much they love/hate their instrument or Ricks in general. Body: there have been 360-12s with 330-style body at times (George Harrison's prototype, anyone?), but usually they come with clearly different bodies. When a 360 "apes" a 330, it has deluxe features like body binding and triangular position-markers (and when not, the triangular position-markers remain and the binding is in the slash soundhole). So a 330 always has "dot" position-markers and no binding. Electronics: a 330 always has a mono-only output jack, and it is a crucial difference with 360s, which have always a second, stereo Rick-O-Sound, output jack together with the usual mono one. The rest is identical, at least in the normal production models: three-position pickup selector; two tone and two volume controls (even in 370/12 guitars with three pickups, the neck and middle ones sounding always inseparable), with a fifth small knob acting as a secondary neck volume control, wired to allow a precise balance among pickups in the middle position of the pickup selector; and High-Gain pickups (and I mean really high gain, almost a destroyer thing). High Gains are a late-1960s design. The Beatles and The Byrds used Ricks with "toaster" low-output pickups which sound slightly brighter, but Rickenbacker mounts them now only on the 660 model and on infrequent, costly reeditions of Beatle models or signature limited-edition beauties. Of course, Rickenbacker offers "toaster" pickups as an aftermarket replacement, although Rickenbacker is not the nicest company, it seems, when trying to purchase things like pickups or "R" tailpieces from them (because they fear people trying to improve cheaper Rick-like guitars with the key components of a genuine Rick, and they have lawyers protecting their property). The difference between "toasters" and High Gains is, when talking about 12-stringers, very hard to notice ("toasters" are for a Byrds-y sound, while High Gains define the R.E.M. sound; both are really good). Four final notes: a) 12-string 330 and 360 Ricks come with a six-saddle bridge, and there is a ten-saddle bridge available as an aftermarket replacement (mandatory, IMO: my 330/12 now has it); b) the neck is narrow for a 12-stringer, although there has been too much unnecessary drama about it on the internet, and I myself can play mine with my big sausages; c) be prepared to replace the "R" tailpiece when it breaks after 20 or 25 years of bearing 200 lb. of tension; and d) an advice: use Pyramid flatwound strings, Pyramid sells a set intended for 12-string Ricks and Tom Petty (among others) finds it key to a good Rick 12 sound.