Simplify the following text for a Grade 5 native English-speaking person.
Original: Previously a part of multiple GT racing series including the now defunct Group C class of the All Japan Sports Prototype Championship , the Suzuka 1000 km as of 2006 is now a points round of the Super GT series , and is the only race of such length in that series .
Simplified: The Suzuka 1000 km is a round of the Super GT series , and is the only race in that series of that length .