1969 dodge dart rear rim size

Well...time to order tires and rims. Have gone through a ton of web sites and get conflicting remarks. If guys that have a 69 dart can chime in ...it would be great. It appears 70 and up darts have a little more room then the 69 and down darts. My question is will a crager magnum rim in 15x8 with 245/60r/15 BFG fit. It has a 4.5 offset or am I safer going with a 15x7 with the same tire. Most say a 255/60/15 will not work on a stock 69 dart rear without rubbing on the lip. I am using xhd springs from mopar with a stock 8.75 with new Dr.Diff axles in the LBP. Also ... what do you guys think about using a 15x6 on the front with 205/60r/15. Anyone have clearance issues. Thanks again guys ...great site