the 3 measurements you are talking about are as follows

preload... thats the effort to turn the pinion without the diff installed, this ones not critical if you dont pull the pinion assembly out of the housing the rough check that I use is to try and spin it from the flange end by hand it should offer some resistance and not be lumpy when you turn it and when you whip it around by hand as fast as you can it should only complete about half a turn when you let it go.

Runout. This one counts... Put your DTI on to the back of the crown wheel along the axis of the axle and turn it slowly watch for needle movement, without my books in front of me +/- 2 thou is all you want and less is better. IT also pays to check for radial run out as well. check it before you pull the diff down and after you assemble it again.

Backlash, thats the free play between the crown wheel and the pinion, push the crown wheel against the pinion in one direction, setup your DTI running along the circumference of the crown wheel and rock it back and forth from contact to contact against the pinion gear, observe the DTI.

When I do over a rover diff (assuming its not totally FUBAR and Im just reworking it as an overhaul, putting new spiders in or putting in a locking center) I use this roughly this procedure

check all the measurements
blue the diff and check the contact pattern (hi res digital photos are great here)
put the new guts in and set it up to "feel"
meaure it, adjust untill the measurements come up as per the pre work specs
blue it
adjust it till the blueing pattern is as close as I can get it to the prework pattern.

leave it sit overnight so all the locktite can cure or lockwire the bolts and fold up the tabs on the lock tabs.

you dont have to blue it if your just redoing the old diff but you should as they will wear into each other and setting it up to new specs will throw that off and then it will whine like a pommy in an Australian summer being made to drink a cold beer.

I use +/- 1 thou for runout
+/- 5 thou is optimal for lash
preload I dont touch unless Im replacing the pinion and then your into a whole new ball game and you need to do about 5 more measurements as part of setting that up and shimming it into position....

For those interested in seeing one done in perth when I get there for xmas I'll be doing one at or near dads place (carine) and your welcom to come along.


Best of luck

__________________
Dave

"In a Landrover the other vehicle is your crumple zone."

Big Red '03 D110 Extreme (TD5manual chipped)
Fozzy, 2.25D SIII Ex Telecom Highside Ute (bye Kermit)
T4 Diagnostics (sorta)

For spelling call Rogets, for mechanicing call me.