“On The Edge: The Spectacular Rise and Fall of Commodore” tells the oft-missed-by-the-geek-historians story of Commodore. The web site has some free chapters, including one describing the creation of the Commodore 64:

If you’ve ever wondered why the C64 has the same case as the VIC-20, it’s because we didn’t have any time to tool anything up. We just put it in a VIC-20 case and spray painted it. Everything about the Commodore 64 is the way it is because of just an unbelievably tight time constraint on the product.