I've been asked about what changes that I have made and what would be manditory, and what would be nice to have. So here is my thoughts:
1: Get the OFNA 40066 150cc tank - will bolt right in, no drilling chassis needed.
2: Buggy Gearing in the diffs, 43/13. Stock gearing is fine for playing in the parking lots or running a .28 RTR, but it is way over geared for racing. Acceleration out of the corners in the infield being where it is less than optimum. 41301 Bevel Gear, 41302 Pinion Gear
3: Change the brake disk to a metal vented with the option pads 36659 pads, 49009 disk.
4: 10 Degree C-Hubs - this works with the chassis kick up to get you in the right range for steering with out chewing up front tires. 41533
The following is what I have used and am happy with the results
5: Front 2.5mm sway bar
6: Lowered engine mount #41337, this also keeps the engine located better for 30/45 min mains.
7: Bearings in the steering linkage. Make sure the small washer is in there.
8: If you are not running the stock body, look at using the rear body mount off the DM-1. It moves the posts behind the wheel wells, so not as much flex with the lighter bodies. If runnig the kit body, use the standard mount.
9: I've put in some light weight parts, turn buckels - pivot balls - pivot pins .... but all really do not make the car faster.
Things that I have tried and need more work or different parts.
Adding a second brake disk set up. This is a standard for the DM-1, but the clearance to the flywheel is tight. I used the narrow JLR light 34mm flywheel and the brake disk still got into the flywheel. If you turn the brake disk down to clear, you are into the slots, so not a good thing. I need to work with this.
I have some of the hinge pin holders coming, and know that the rear does not work with the GT chassis which is flat in the back, vs the kick up in the off road version, but there is some speed to be found for racing with some changes.
If you try and gear the car with the stock diff gears, you will end up with the 14/18 pinions (smallest option). With this, you will need to grind down the right rear engine case by the screw to clear the rear drive shaft. I also changed to a button head screw for that spot, but you could still end up with a groove in the drive shaft. Watch, rotate if you see it. I know the factory is working on a fix for this.
I would also like to try a few spring options, but have not taken the time to see what is out there that might work.