Hi ALEX. Regulations for the 2023 Sixties Endurance series are here:
https://www.dropbox.com/sh/zy5f11f2p...rojet.pdf?dl=0
You can read: "International Grade IT C-D minimum Drivers licence A national highest grade licence will be accepted for entrants racing in their own country providing the licence has been issued by the organising ASN."
Again its worth a phone call. Have fun!