Wheel Backspacing?

I have a 69 camaro with centerline drag Auto/Drag wheels and am wanting to go to with a new set of Crager SSs. I have read that to go with a 15 inch wheel backspacing should be 4 and half inches for ideal fit, but when you go to buy them, this backspacing is not avaible on JEGs or summit. Does anyone have any light to shine on this situation.
Thanks,
Andy

PS i would just go check the stupid backspacing on my cars current wheels but im in the army and my car isn't with me (most unfortunate) and won't be for a fairly decent chunk of time

give jegs or summit a call, or write em an email. some of there inventory isn't always listed, just depending on what catalog you have