This car had the straight 6, DOHC Weber carburetor engine that was derived from the engine in the Maserati 350S. It was fuel injected after 1961. It made 220 horsepower and was paired with a 4 speed transmission. After 1961 it was a 5 speed transmission plus reverse.
The cars were sold as either 2+2 coupes or 2 seat Spyder convertibles.
The 3500 GT was introduced in 1960. The 3500 GT spider designed by Carrozzeria Vignale was rare, with just 242 of them made. The two variations of the GT version of this car were the 3500 GTi and 3500 GTis.
In all, there were 242 Vignale convertibles and 2000 coupes produced. 1961 was the most common year.
As you can probably imagine, these cars are very rare and quite collectible. You aren't going to find these at your local used car dealer, unless they happen to deal in exotics. Try looking on eBay, they have just about everything, including a Maserati 3500 at times.