Factory Wheels should have an ID stamped into the metal, similar to the attached picture (borrowed from an earlier thread). The "8" is the year, "M" is the manufacturer, and the "D" is the Month (in the example shown), for April. Sometimes, instead of a letter for the Month, numbers have been seen (1 for Jan, 2 for Feb, etc.
Per the 1968 Ford Car Specification Book, available tires are shown in the second picture attached. The third picture is from the Salesman's price book, dated September 22, 1967.
Hope this helps.
Bob