centering rear end

the springs are good,not sagging,and don't appear to be bent.Measured from the perches to the backing plates and they are the same.No sign of frame damage.Have thought of putting in the off set shackle kit but don't plan on going any wider and have 3" exhaust and off set shackle won't clear the exhaust,close now.I've replaced the shackles,previous owner pieced old ones together,used heater hose as shackle bushing.Thought I'd just split the difference by moving the perches,have plenty of room to the leaf springs3/4" and it's the sameon both sides the tire I'm using don' bulge on 8"rims,had them on my mustang.MT sportsman radials 26x10r15s