Nevermind. I read more and found that 1973+ is Group 9, not Group 2 rules that I just posted. Group 9 just says: Approved tires: Suitable and appropriate slicks and treaded tires.
Is anyone running a Series 2 air-cooled FSV with SVRA? The SVRA tire rules lists only the following for FSV:
Approved Tires: FB: All Monoposto approved tires Hoosier: 21.0x9.0-13 R35B, 23.0x12.0-13 R35B F1, F2, F3, FSV: Dunlop: L, M, Post Historic CR65 and CR82 Avon: All-Weather H-003—H009
However, they link to Monoposto and that says:
D. Tire size, compound and type (treaded or slick) are free, but may be dictated by the sanctioning organization. If allowed, Series 1 cars without wings should consider using treaded race tires to be grouped with open wheel cars using similar tires.
TIA