The federal code is interesting because in some places it specifically says "commercial" and in others it does not use that adjective.
Irregardless, if you want to go by state laws, I've found this link to be helpful:
http://www.wecamp2.com/size.html
Also, when I was referring to being pulled over, I was commenting on how it's unrealistic to expect every law enforcement officer to know every law (state and federal). Educating them on the spot can sometimes be difficult. I was saying that I think the chances of getting pulled over for length are a lot less than the chances of getting pulled over for not stopping at a weigh station, which I would consider to be pretty low odds all the way around.
When you say "Gruman", do you mean a Grumman bus? Is your cost including the truck? Sounds like you've got a great setup for a very low cost.