Tire size for 72 Duster

I am going through the same thing with my 72 Duster. I currently have 14" stock ralley wheels but would like to go to 15" Cragers but not sure what size to use. I have the small bolt pattern and my back space is 3 3/4". I asume your is the same. I hope I can find some info by keeping tabs on your thread. Hope you don't mind