Mike pointed you to the correct area re: frame. As a point if we copied all the rules in the Modified Category to the Classic Category the rule book would be much bigger than it has to be. A simple sentence referring the builder to the Modified rules, which the Classic classes must follow, precludes this requirement.
My sentence, quoted by you, refers to your original plan to build a Classic Gas Coupe, OEM frame required.. The frame moves the car to the Altered class, any frame can be used. If I am correct you stated that you wanted to use EFI in your original plan. That is what I suggested would move you to Modified Category, Altered classes.
DW