According to what I could Google, it was a DC8-63. Standard seating capacity would have been from 180 to 220 for that model per Boeing. So they were really packed in, and probably had a full load of luggage and equipment as well. If the model info is correct, the plane wouldn't have been that old. 63s were built between 1967 and 1972 and many have racked up over 100,000 hours in the air.