At the time Breedlove broke 600mph, the FIA refused to recognize it as a record not only because the vehicle was not wheel-driven (they have since changed this rule), but also because it had only three wheels. But because it had fewer than four wheels, the FIM did recognize it as a record.
IIRC, the record for wheel-driven vehicles is somewhere in the mid-400mph range.
Wiki says it’s the Poteet Speed Demon at 439.
He runs a Kenny Duttweiler turbo small block that makes some serious hp.