Grimmey,
Do you have a Cuda or Challenger? Like Wes said, I've heard that the Challenger has slightly larger wheelwells. On my Cuda, the 335 was pretty tight in the stock wheelwell and this was without any suspension on the Cuda (it filled the whole wheelwell). With the lower bars in the stock position, you *might* be able to fit 315s, but I'm not sure. The problem is you can't "shim" the lower control arm over like XV did, because there are no spacers between the arm and the bracket on the Air Ride control arms (XV has different lower control arms). The bushing fills out the whole bracket (see attached picture). So that being said, you do gain around 3/4" - 1" just because it's a round bar versus a leaf spring. If you move the front mount over to the frame then you can gain around 2" (you can see the original leaf spring mount holes in the picture).
If you're willing to pay shipping, I could send you a 335/30/18 that you could use for mockup purposes. Send me a PM or email if you're interested.
Travis
72 Cuda