I do not know who Ken Anderson is. Other than he is the person who built the car. I do not know if he owned or worked for a company or if he worked in his backyard. But Ken Anderson built your car.
The rules and regs do say you need a Passport, Passport card, enhansed drivers license or other form of ID (all of which require a passport) to return to the USA. And yes you can get back without it but you risk a hassle. And ONLY a passport is acceptable to get a Mexican Visa (or FMT).