I am interested in knowing what backspace folks used on 275x60 or 275 x 50 fifteen inch rear wheels... that worked out well, with standard ride height (or lowered) and had no rubbing. I was thinking about going with 275x50 on the back and a 60 series on the front of about the same height. I think the '69 model year is more popular, expecially among the Camaro crowd, because it has more room for wider tire choices.

Until you measure ride height per the manual, you can't say Eaton did you wrong. I think Eaton does a good job on springs and probably the best vendor going for springs. Mike at Eaton tech support will give you all the time you need to set things right and make spring selection. And he knows his stuff. He knew what springs were in my car without seeing the car and they had been swapped out by previous owner decades ago. He even described what I would find because the aftermarket swap was fairly generic years ago. Lots of these cars got lifted in the seventies by changing or re-arching springs. Others got the foot tall shackless, lol. My project has aftermarket springs that jacked the rear end way the heck up.

So to say it was fine before you put in the Eaton springs doesn't mean anything, because you don't have F70x14 tires, standard rally rims and the original springs. When you go to Eaton for spec springs for the bird, you get a standard spring that will set you to stock specification ride height unless you ask them for an alteration. I wouldn't raise the bird to fix tire issues. Lowering can improve handling, but I think the '67/68 really calls for the wheel openeing to frame the tire evenly, so I would leave it correct.

For the tire to stick out beyond the quarter means the offset is inadequate for the tire selection. Getting by without scraping before the spring change is likely from the car riding too high. With the car at correct height, the oversize tires are not tucking under the wells.

Anyway, don't trash Eaton without calling for help.