Finally got this pinewood derby thing figured out now that it's the last year.
My son designed his entire car himself in TinkerCAD and is 3d printing it. Which is great because I have a 3d printer but I don't have any woodworking tools except for a crappy hack saw that I have actually used on a pinewood derby car before and it was terrible.
He's printing the body in woodfill PLA which is about 30% wood fill so it can be sanded and stained. If it turns out I'll try and post a pic.