If the title is in the guys name it may not be a problem. However, if he has never had the truck he wants to trade you in his name then ruuunnnnn....or, if he will go get it titled in his name and then sign that title over to you its a whole different ball game. Again, is the title currently in HIS name?
....and since you've been given the run around for so long, whats wrong with going to court. I'm not a judge but its seems the guy will have to pay up/back or finish your truck by a dead line. Mmmm, maybe some other option is the answer?