The GS became it's own model line in 1967, after it enjoyed success as an option package on the Skylark in 1965 and 1966. The model names were the GS 340 (or California GS) and the GS 400 (numbers denote the engine size). This name change was probably due to marketing; The muscle car craze was taking off, and the Skylark line didn't have a real following with younger drivers. The "Buick GS" definitely has a nice ring to it.
Styling didn't change much from the Skylark. The rear wheel skirts were removed, the grille had a thicker horizontal bar, and the rear tail lights were enlarged. The front hood scoops were now facing the front but still inoperable. A three speed automatic was a new option.
1967 GS 340
The GS 340 is sometimes called the "Junior GS", and was marketed as a cheaper version of a GS 400. The only exterior color options were white or platinum mist, with both having red rally stripes and red lower molding. The GS 340 sold poorly, probably due to the fact that the base price was just over a $100 difference, and the limited color choices.
1967 California GS
The California GS was only available in California, and was not advertised nationally. The marketing idea behind the California GS was to build a strong looking muscle car, but have it powered by a smaller V8 engine, giving it more reliability, lower maintenance costs, and a lower overall price. Options were kept low to keep the price down, but the California GS did have all the extra trim that the GS 400 had, and it had special "California" badging. These badges today are hard to find and highly collectable.
1967 GS 400
The Buick GS 400 is a true muscle car, since it is a mid sized car with a large V8 engine. It is technically the only true muscle car Buick built, and in the later years it was definitely a formidable foe at the race line. The previous Skylark GS models had a 401 ci V8 engine (Nailhead engine), but Buick introduced a new 400 ci engine for the 1967 model year. This 400 ci engine had larger valves and better exhaust headers, giving it better efficiency.