We allow Mustangs to run the same class they would at the Roundup event in Steamboat, but it's not required.  We also allow anyone to run the same class they normally run at SCCA events so they don't have to come up with another set of class designators.  While we prefer that people use large number and class designators that are compliant with local SCCA rules, again we do not require it.  We do require that they be legible from a reasonable distance, while the car is moving.  Using high-contrast colors relative to the car color will go a long way to achieving that goal.