If you want to make weight I would highly recommend adding a driver figure. The amount of lead you have to add to the chassis is ridiculous; whoever made the VTA rules is a chump and must sell aluminum suspension arms.

I would only worry about the motor you use if you are planning on running legit VTA at a big race. I personally have the D3 25.5, am underweight by 70g, and have male genitalia painted on the back of my car, none of which are VTA legal.