Rear axle adjuster on left side??

My axel adjuster is on the left side. To my understanding this is wrong. The rear is a 71 duster 8 3/4 in my 65 barracuda. After fixing the reverse wheel hop issue i noticed a slight vibration at about 3000 rpm and up. The axels do have more end play than they should have almost .020. I know it should be about. 006. I am thinking who ever put the rear in the car goofed.
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