Hi Magnus
Welcome to SM.
To answer your questions:
There is very little difference between the 2.0 GT and the 2.8 GT other than the engine and related components. The 2.8 GT was available in both manual transmission and automatic whereas the 2.0 was manual only. All versions of the 2.0 have a 6 speed gearbox but only the GT version of the 2.8 has the 6 speed, pre-GT versions (first series and MY95/ABS have a 5 speed gearbox). The 2.0 develops 306bhp and the 2.8 develops 284bhp and they are quite different in their characters to drive. The 2.8 is easier to drive as it has more low down torque but the 2.0 is more fun to drive but you do need to rev it more to get the best out of it. The 2.0 GT is slightly rarer with 166 produced compared to the 2.8 with 212 produced.
All GTs have the same brakes, only the Cup version had the Brembo 4 piston calipers although a few GTs were fitted with them by special request and some have been retrofitted, but you'll find most have standard brakes. They are generally perfectly up to the job but uprated standard size discs and pads are available from companies like Tar Ox who also do a full conversion kit with bigger 310mm discs and either 6 or 10 piston calipers.
All GTs had the 17" 7 spoke wheel design as standard, the 16" wheels were fitted to pre-GT cars (first series and ABS models with different designs), although you will see a number of earlier cars with GT wheels fitted as they look better and give more ground clearance for the vulnerable diff oil cooler and engine sump.
Finding a Ghibli in good condition these days is very hard and narrowing down your search to a GT makes things a little harder due to the limited numbers produced, but if you can find one they are the best in terms of build quality and reliability. Beware of cars advertised as GTs that aren't, I've seen many. GTs began to appear in the latter part of 1995 but many earlier cars were not registered for some time after they were built so you will find non-GT cars that were registered in late 1995. The easiest way to tell is to look at the rear differential, if it has an oil cooler attached its not a GT, if it has a large tubular structure around and underneath it and no oil cooler then it is a GT. You can also look at the engine bay, the GT has the braided fuel pipe at the rear of the engine bay on the left side as you look from the front of the car (passenger's side on LHD), if its on the driver's side, its not a GT. Another clue is to look at the left side of the car (driver's side on LHD), if there is no dummy fuel filler on this side it is a GT, this was only applicable to the very last examples though so early production GTs from late 1995 will still have them.
Don't necessarily dismiss the earlier cars though, yes the build quality isn't quite so good and the diffs are not quite as strong but they rarely give serious problems. The early 2.0 cars tend to be very raw in their power delivery, are quite exciting to drive and are quite sought after in their home country.
The best advice I can give is to look for a car in southern Europe where the climate is less likely to have taken its toll on the bodywork. These cars are mechanically very strong if looked after correctly but the bodywork can be susceptible to rust irrespective of age or type, although GTs are slightly better in this respect. Don't use it in the wet or on salty roads and the bodywork should last ok. Germany and Switzerland are also good sources of cars, despite the climate not being very dry they tend to really look after their cars in these countries so you might find a nice one there. Try
www.mobile.de
Its also worth checking out Enrico's Maserati site in the classifieds, there are sometimes Ghiblis for sale there in various parts of the world:
www.maserati-alfieri.co.uk
Here's a nice 2.8GT to get you started on your search:
http://suchen.mobile.de/auto-insera...veFeatures=EXPORT&categories=SportsCar&noec=1
Hope that hasn't caused too much confusion!