Errr...yeah, AR doesn't make those wheels in that size in the proper backspacing. I discovered this a few years ago. You have to custom order them if you want them. I tried some on my car last year and found the same thing you did. I was bummed because I could've had the set for $400.
But the Vintage 45's with the proper backspacing do work:) I've seen several 67-68's with these, including a couple lowered with those same G-Force tires, and they tuck up nicely under the wheel wells.