The GT-37, was actually the all new Tempest GT-37, which was introduced as a mid year car, so they are usually referred to as 1970 1/2 cars, sort of like the 1964 1/2 Mustangs, that are all titled as 1965 cars.
Pontiac marketed the car as the GTO for kids under 30, due to the skyrocketing insurance costs at the time. This car was Pontiacs low-cost, budget minded, entry level muscle car. The standard motor was a 350CI, two barrel V-8.
Marshall