Appropriate Wheel Offset for 18" Wheels?

Those Valiants must have more room than the 70+ Darts. At least my '71 for sure, when I tried a set of 275's they touched the spring and the quarter lip at the same time. They physically bolted into place, but they couldn't be run. I could gain a little room on the outside because the quarter lip is stock, but there's no way I could make a 275 work on my '71 Dart without a 1/2" offset.

And, nice Valiant Tom! :thumbup: