Complex sentence: This will be the first time that a full Super GT field will run in the race, previously, the race was open to JGTC/Super GT cars, but with only a handful of competitors from the Super GT entering.
Split into simpler sentences: This will be the first time that a full Super GT field will run in the race. Previously, the race was open to JGTC/Super GT cars, but with only a handful of competitors from the Super GT entering.