Wheel backspact/offset

[dammstrate]

I have a 65 Sport Fury with old style Cragers on it. Want to get some Magnums, but unclear what size. Current tires are 255/60/15 on back and 235/60/15 front, they will be reused. Pretty sure this is 15x8, but there are two backspaces offered by WheelsVintique, 4/5" and 5".
What would be the normal for a 65 Sport Fury?

 

[cbarge]

4.5

 

[Luke Pokrajac]

I have 15X8 Magnums all around on my 68 sport fury. 275/60/15