We agree to disagree. Fender rollers really work best on thin metal and round wheel openings. The one I tried was not from Eastwood™ and that may have been a small part of the problem....
That roller DOES NOT WORK on A-bodies. They only work on cheap Japanese metal cars. Our car metal is too thick and double thickness where it rubs. Don't waste your time or money on this item!
My 68 GTS had 9.5 wide tires with offset rims, but I had room to spare toward the leaf springs. I don't see why you can't fit a 10" wide tire within the confines of the dart wheel opening.
Yes, I overlooked the obvious, Thank you Johnny Dart. But I have been told that PT Cruiser wheels will bolt up to a 68 Dart, not sure about the offset/backspace.
I think you will find that once you have a good fit on the front, you will be able to use the same wheels on the rear only if you add a spacer. That is what worked for me.
I have 17 X 7's all the way around with no clearance problems (Zero offset) on my Dart. You can go with 8" wide wheels easily with 4.5" backspacing. Tires are 235/45/17
Hope this helps you