Front tire clearance on 66 Dart

Uh, it's less than half that. According to the factory the 73+ track was 59.15", '72 and earlier was 57.74". So that's a total change of 1.4", per side is half that.

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I apologize. I knew 1.5 inches was sticking in my head. But let's not forget this car is a 66. I think you are thinking of 67 to 72. I'm pretty sure the 66 and earlier are another 1.5 narrower. But I can't remember. I know I put 73 knuckles on my 66.