From my experience with the old 103 (F1) I will be looking for a body with teh least downforce on teh front and the most on the rear. Also trying to get less bite from teh front tyres - through different tyres and maybe different inserts. Agree run a little slip in teh diff.
If you can run foams then it will be no problem, just run a hard front (42) and a good grippy rear (35).
The major reason for teh rear grip issue is that there is no rear toe in - try running your touring car with no rear toe in and you'll see teh difference.
For those that can get them hooked up and learn teh driving techniques required there's plenty of cheap fun in store.