That says Pat Pending, right?
An informal guide to narrowing them down to a window of time. If your grill has these cosmetic traits or markings: Vent reads Bar-B-Que-Kettle Patent Pending with small single turn tabs on lid and bowl, plastic or metal wheels/thin whitewalls with plastic hub caps and rubber treads. No thumbscrews. Based on research would place your grill between 1968-1970.