what is the widest rim u can get on the rear of a 63 dart

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I have 7" wide with 4" backspace on my 66 Dart. 225/70-15's with no trimming or rubbing. I think 8 wide would fit but wheel lip trimming or rolling is necessary.
That looks tough, yours sits about 2" higher in the rear than mine (stock height) which will help. It's a good look...