There are plenty of period correct classes which allow a slick tyre, for example the Heritage Touring car class at the festival allow slicks because that is what those cars ran in period. Certainly there are plenty of HSC compliant cars which would have run slicks in period as well. Don't forget the proposed HSC cut off is long after the HMC cut off and well into the slick use era. I think it is something that should be considered, not dismissed because HMC don't run slicks.