wondering if these wheels will fit my dart

I would say 4.5 inches would be the max without moving your leafs in some. Even then I'd suppose the rubber would sit pretty close to your leafs. Bearing in mind the max you can move your spings in without going inboard of the frame rails is 3/4" (I have an 1/2 inch kit from Dr Diff, but Mopar relocation kits allow 3/4 in with some clearancing the frame rail for the spring eye bolt), with 5.5 backspace rims you'd be 1/4 inch closer to the relocated springs than you would with stock spring location and 4.5 backspace. Perhaps too close for comfort?