the back lash for gbr 4.10 gears is between .008" and .010" (that's 8 and 10 thousands).
the pinion height is determined by your carrier housing. the earlier housings usually run around .054" to .058". the later axles uses a must taller shim height typically around .080" to .084". my 99" used .082" in the front and .078" in the rear. keith is correct in using your original shim to start, but more shims will be needed to be correct.
pinion preload should be as close to 25" lbs. as you can get.(25 inch pounds with new seal).
when i set up a gear set, i drop in the stock pinion shim and add .020 to .030 shims (usually (2) .015" or (2) .010" shims)
use an old pinion race slightly ground as a set up race and drop the shims, race, bearing, and pinion gear into housing. place the carrier in the housing and check the height where the top of the pinion gear meets the ring gear. what your looking for is the top of the (p) gear to sit level with the inner edge of the ring gear.this will get you started. once it's close, set the preload, backlash, and roll a pattern.
when the pattern looks good, disassemble and redo with the new pinion race.
things to keep in mind, when pinion to low, add shims on gear side and remove an equal amount of shims on the flange side. this keeps the preload the same when changing the gear height. and for the pattern, i 've found that the yellow pattern gease mixed with a little white lithium works better than the prussian blue.