Complex sentence: A production run of 500 units is required under the Group A "Evolution" special regulations, but an additional 60 were produced and held by Nissan to turn into race cars, giving a total production of 560 units.
Split into simpler sentences: A production run of 500 units is required under the Group A "Evolution" special regulations. An additional 60 were produced and held by Nissan to turn into race cars, giving a total production of 560 units.