[eclipsegsx1736]

I'll chime in first and add a few things.

1. The 1g and 2g chassis' are weak and have quite a bit of flex, like you said a rollcage is a pretty good way to help this. Not too much data on foam filling though.

2. 1g suspension is a McPherson setup which is crappy. 2g's get double wishbone, which is the best suspension a car can have (look at F1 cars, this is basically what they use). McPherson CAN work well though, but the geometry is inferior to others. Both the 1g and 2g obviously are undersprung and underdamped from the factory. Besides stiffer shocks/springs and swaybars (add a rear only first, then add a front if you still need it), the stock bushings are very weak and should be changed out for a full urethane kit (energy suspension or Prothane).

3. Very few people upgrade the diffs on AWD DSMs especially for road racing. More for Auto-x. Road racing speeds are high enough that you won't be spinning the inside tire that bad. That said, a Torsen type like the Quaife WILL improve power-on grip, but will hurt you when off-power. The LSD doesn't spin freely when off power. Not much info on changing the center diff out on AWD DSMs.

4/5. Looks like you got that covered and what you need to do. In fact, looks like you got most of this pretty well researched.

Obviously cooling issues are a problem too (remove your A/C at least, bigger radiator, better ducting, avoid a FMIC if possible or get one that flows through itself well) but we're talking suspension-only issues. 1g's also have the active toe which should be eliminated. If you do all this, along with the obvious things like wider wheels and tires, camber settings, etc you'll have a hell of a car.