Make sure you have either a decent caliper or micrometer. After you remove your clutches and spacers from one side, mic them then stack them as was suggested above (clutch, spacer, clutch, spacer - factory setup is clutch, spacer, spacer, etc.). When you get close to your original measurement, add shims to bring the entire assembly to what you mic'd them at after removing. Then, reassemble the entire thing, making sure to cuss repeatedly whilst trying to install the spring! Anyway, I did this to my differential waaaay back in the early '90's and I noticed immediate improvement when I too the car to the track!
Good luck