As I understand it, the cars need to be 'mass produced' to a certain extent.
IE. Can't drive a Pagini Zonda, Mac F1 etc.
The S-Tune and R-Tune are really lower than the N1.
N1 has NO radio, NO this, NO that.
Does have Carboin Fibre under trays, front lip, Carbon Bonnet, etc etc etc.
It's about choosing the highest spec you possibly can, and then building that into a race car.
Or, replicating a lower specced car INTO the higher spec, using all the higher spec parts. must be genuine parts though.