If it's not road legal, then it's a race car. But race cars are subject to limits on weight, engine power, and aerodynamic devices. So a car that's not a legal race spec and impossible to register for the road (in its current form) is neither fish nor fowl. I'm sure that if Cadillac were to show up with a derestricted, weight-gutted, and competition-illegal version of its IMSA GTP, the result would chop 30 seconds off the Ford result.
As always, I think there are basically three types of cars that turn these stunt laps; cars that are road legal, cars that are race legal, and cars that are neither. The challenges of competing with constraints means that my personal affection is for the first two categories. More than anything about the new Ford record, I'm impressed by the driver. Watch the in-car video from this run and marvel at his reaction times and apparent knowledge of every single curve on the Nurburgring before it even arrives.
Best Regards,
Tim