Shimming a 10 bolt rear end

[ppscugog]

I have an 87 GMC 4X4. It has a 10 bolt 8.5 inch 28 spline rear end with a 3.42 gear ratio. The pinion shaft failed so I bought a case from the wrecker and bolted my ring gear on to it. I'm having problems shimming it for backlash. In order to get the correct backlash (.008) all of the shims need to go on the ring gear side (drivers) with no shims on the pinion side (passenger). I did not touch the pinion setup. Something is screwed up. Any driveline experts out there? This truck is just for farm work so if I can't fix it myself it gets parked. The used case I bought may have been from a 77 Chevelle, guy at wreckers wasn't sure. Maybe 10 bolt car and truck rear ends are different?