I think the first thing is you measure the backlash at maybe 4 points equidistanct around the ring gear & note the tightest (smallest) dimention & record that number. The used pinion bearing that is behind the beveled gear teeth would need to be pressed off & slightly ream the ID so it will barely slip on/off the new pinion shaft till you get the right shim pack thickness figured out that goes between the bearing & the gear teeth flat to get the pattern right. I'm in the same boat & there some internet sites that have procedures. I'd try Randys ring & pinion for a start. the ring gear bolts are left hand & you want to deburr the new ring gear with a whetstone so it sets dead flat when bolted on. The 489 may not use shims & you just torque the pinion nut & the solid spacer has been highly recommended rather than the OE crush sleeve. Here's a BTT for ya & others will guide you better