Loaned a buddy of mine 350 plus $100 interest. He signed a piece of paper saying he would pay me back in a certain amount of time he has not paid me b

You can sue him for the breach of contract, but you may have a hard time since $100 interest for 2 months on a principal of $350 is about 170% annually, which is clearly usurious.  From what you've written, I see no basis to sue his wife, or to attach any vehicle, let alone one he does not own alone.  Absent a contract that specifically allows you to do so, you generally can't attach any assets until and unless you obtain a judgement on your claim  from the Court.