Update time!
...And this time the news isn't so good. I've tested the car on carpet last weekend. I was expecting the car needed a few tweaks to work well, but it was an utter disaster when I arrived: The car was completely undriveable. A lot of setup changes were made: Mini Pins on the rear (to keep it stable over the low-bite sections), much harder front springs (to reduce diving and grip-roll), 5mm limiters in the front shocks (to reduce grip roll and add rear stability), a lower ground clearance (to reduce grip roll), 50g extra weight on the back (to keep the car from diving and making stoppies). It all helped, but it wasn't very good yet.
Since the car wasn't working, I went all for broke and fitted the 4WD front end. I tested it in the break between qualifying and finals, and it went quite well. The geometry with the 4WD front wheels is more natural, and it showed. It also seemed as if the wide tires were just giving too much sideways bite to the car. It wasn't very confidence inspiring yet, but by now I know the car good enough to race with it.
I had been having a few breakages, and the bad luck continued with loads of mechanical problems. All in all, the only heat I finished was the last final of the day. The car was quick enough to become third in the D-finals - I'm no pro, but I should've at least managed a high C-final with a decently set up RWD.
It has taught me perhaps next time I drive a car for the first time on a surface I'm not very familiar with I should try to find some time for a free practice day with the car, not enter it in a race!
Also, with the handling the car showed by the end of the day, it's clear that the car will need a lot of setup work and some design changes to work on carpet.
Stay tuned for more updates, they're due soon!