The 17x8's should fit. Ideally, they'd have more backspace in the front. They should fit though if you don't go too crazy with the tire. They should fit ok in the back, same deal with the tire (on a Dart anyway, they'd be fine on a Duster/Demon).
I've tried the 17x9's with 5" backspace from my Challenger on my '71 Dart in the back and my Duster in the front and back with 275/40/17's. They hit the springs on the rear of the Dart, and were right up against the quarters too. With a 1/2" spring offset they might fit, but you'd have to trim the quarter lip for sure on a Dart. A 255 would fit easier on the quarter, but I still think you'd need the spring offset to clear the springs by enough. On my Duster they fit with a 1/4" spacer to keep them off the springs, they just touched there. Again, it'd be good to do at least the 1/2" spring offset for space, with that in there you'd be clear on the springs and the quarters with no issues. Lots more room on a Duster vs a Dart.
On the front you need more backspace. With 275/40/17's there's no way you'd keep the tires from hitting the fenders in the front, to go that wide you'd need the 5.75 to 6" backspace with 17x9's, whatever you could get away with before tie rod interference. I don't think going to a 255 would help either, you'd still be into the fender. And if you're going to go smaller than that, you might as well get the 17x8.