Maybe a T3 or T4 base, due to their original size? They start as a ~2m long projectile and then extend their wings. It makes me think the wings wouldn't have much in the way of structural reinforcement. The lack of self defense systems, etc, make me think it'd be right to have these be a bit more fragile. They seem less resilient than a Mindy, which is the T4 example.
My recommendation would be a T4 base with a T3 DRv3 rating, but I'm curious what Kai/Syaoran has to say.