I've had my July 28 for 30 years and seldom see 28 fordor's with LS cowl vent at National Meets. I don't think they had right vents. Factory photo's highlight left side vents, upside down handles, post light switch and celluloid visors. (never saw a celluloid visor either)
http://www.maffi.org/factoryphotos/ I could be wrong?
Brian