The 8" wheel makes the section width 1" narrower on the tire. It makes a difference. An 8 wide wheel will allow a 275 tire in an unmodified Dart rear wheelwell. A 9" will rub without work.
But so we're clear, a 275/40/17 isn't recommended for an 8" wide rim. Smallest recommended rim width for most 275/40/17's is 9". So if you put one on an 8" rim you're squeezing the sidewall quite a bit. If the point of the wider tires is better handling, cramming them on a rim that's too small will somewhat defeat that purpose. Better to run 255's and not get the additional sidewall motion.