The wheels are 0 offset with 4.50" of backspacing. The difference is the wheel is larger than the rim width - 9" vs. 8", so on an 8" rim, the center is 4.5" from the back of the wheel with 0 offset...I did verify the measurements...
May i ask where the were rubbing? I'm considering a set of 17 or 18x10s for the back on my 70 mach. Was the offset just right for the tire to line up with the edge of the quarter lip? I'm guessing it was rubbing the wheelhouse but thought i would ask. What offset were those 18x10s? I wonder if the 70 cars have more room out back than the 68. Seems they do everywhere else.
Allowed? Some people think it is not safe and I imagine some racing organazations might frown upon it as well....but if it is done right by professionals like www.weldcraftwheels.com then at a minimum the modifed wheel is just as strong as the original. It is also somewhat common for people to widen wheels.
Yeah, 'banding' of wheels used to be common over here, but if done badly it is dangerous - how can you tell, as a buyer of a second hand wheel, or an annual inspector if it's been done right?
If you've got confidence in the guy that's done it, and you don't have annual inspections, go for it!