This is a camper shell for the 1964 Chevrolet C10 Pickup pinewood derby car shell.
With this shell, the truck is far too heavy to stay under the 5 oz. maximum weight limit, so you wouldn't be able to race with it, but it's fun for show. You could potentially race the truck within the guidelines and just add the shell for fun.
Just glue everything together and drop it in the bed of the truck.