Race is later tonight, but here's what the car looks like:
I did the cutting and sanding, and my son did the spray painting and 'stickering'. Ended up going with a screw-on weight system that I found in a hobby store, versus drilling and filling. It ends up weighing 4.9 ounces with the extra weight, so that's good.
The only problem we had was when I was nailing the axles into the wood, the wood around the pre-drilled holes started to chip off. So I'm not sure if it is as aligned as I'd like, but we'll make do. I also tried to smooth down the wheels and axles a bit. Should be fun!
Thanks again for the advice!