Yeah that is a good trick, to elaborate you take the best two used friction discs from your old clutch pack, and re-order the discs friction-steel-friction-steel instead of the stock friction-steel-steel-friction arrangement. Then use the largest shim possible when you put everything back together (basically the largest one that will still allow you to get the spider gears back in).

You can also get an S-spring from an F150 which is a bit stiffer and will put more preload on the trac lock clutches.