Tires Tires,

Hello, I just got back to Toronto to work on the 64 Valiant , it has original factory steel rims and pristine hub caps, the tires are sears radials approx.40 years old, look great no miles on them but I'm sure hard as a rock, they only have two numbers on them 175-13, no aspect ratio, Before I run out and buy new tires , I was wondering if any of you have any suggestions, like a size change etc.
Thank You