Complex sentence: The GTV6 was a very successful racing car; the 116 type chassis developed for racing since its first outing in the 1974 San Martino di Castrozza rallye.
Split into simpler sentences: The GTV6 was a very successful racing car. Keep in mind, the 116 type chassis were being racing developed since it's first race outing in 1974 San Martino di Castrozza rallye.