Here is a chart that gives you various tire width and diameter for 15" rims and common aspect ratios. Most common size back then was 6.50 x 15 which was 6.5" wide and 26.5 inches tall. That is close to a 190/75 metric size.
I also am posting a link to the tire rack info site, VERY good education on all things related to tires and wheels.
http://www.tirerack.com/tires/tirete....jsp?techid=46