Stock springs are quite soft imo, I got the V one springs for it. There are 3 spring rates, Gold is hard Black is Medium and Silver is soft. Also the front springs for the Vone series are shorter then rear. I was running 60wt oil, but it depends on your track or where your going to run it. Also try and use same brand of shock oil if you experiment with the weights to keep it consistent.

Re header of a aftermarket tuned pipe, very important to match the ports. You will find the port on the header is always smaller in length to the motors port. So you just need to machine it a little to help with the gas flow. Another option part I bought is the special clutch KC45, supposed to engage a little higher rpm and better then stock alloy clutch.

I forgot to mention also gearing. GXR motor is quite torquey and you can pull taller gearing very easily, go up one tooth each on the 1st and 2nd gear on the clutchbell. If you want more you can change the bevel gears on the Diffs from 40t to 39 if you want.