I know that original tires are F60x15 and the consensus is that the Goodyear Polyglas GTs have the tire size in raised white letters/numbers on sidewall. The Kelsey Tire website says they were used exclusively after 1/1/70. My spare is original and does not contain the tire size on sidewall. I am torn between getting a matching set to the spare or a set with the tires size on sidewall. What are the odds that originally the spare would not match the tires on the car? Anyone ever seen this tire used on a 1970?