A 275 is pretty big on a 6.5" wide wheel- you really should have them on an 8-9" rim. A 6.5 is going to pinch that tire down to the point where the tread and sidewall are going to be pretty bowed, which is going to affect wear and bead seating...
And double check that backspacing, sounds a little much to me for a stock rim. Have your springs been relocated or tubs/minitubs been installed? Where is your ride height?
I'm pretty sure you can fit a 275 into a Duster/D.S. rear wheel well but at that size you're going to have to be pretty exact with the sizing and backspacing of the wheel for your particular car- production variances are going to throw things off- what worked for someone else may not quite fit yours when things get that tight.
