Only overheated my car once today!

Drove my car for about an hour in downtown Toronto on a 25 degree C (77 Fahrenheit) day and it overheated again. Only happens when it's in traffic. Should I look into this or is this just par for the course with a 45-year-old big-block car without electric cooling fans?

Radiator is brand new but water pump is pretty old. I'd really rather not spend a bunch of money on electric cooling fans if I don't have to.