rear tires not centered in body

Sorry, when I said the rear end was centered, I mean that the center of the housing is centered not the pinion. Which is a little offset. The spring perches are 44" apart and the same length, there is just enough room for the U bolts to fit in between the pad and the weld on the flange straight up and down. The axle looked to be stock, with no re-welding or grinding marks, but it maybe.

Were the tolerance is on the flat side on the fender, the very top of the arch.
This is the combo that, most here, are running with a 4.5" backspace, I measured the backspace and came up with 4.75" with the 255's