Complex sentence: The 288 GTO started out as a modified version of the 308/328 to hold down costs and to build the car quickly, but little of the 308/328 was left when the 288 GTO was finished.
Split into simpler sentences: The 288 GTO started out as a modified version of the 308/328 to hold down costs and to build the car quickly. But little of the 308/328 was left when the 288 GTO was finished.