Am I missing something here?? Why spend $3500.00 and a car to get a race car that you have no interest in racing?? Why not just spend the $3500.00 on the Duster and make a nice driver out of it??
IMO, this hobby requires patience, and lots of it. Anybody thats into it to make money is in the wrong hobby, especially in this economy. I wouldn't have the cars and stuff that I do if I wasn't a very patient man, waiting for the right deal, never just buying something at face value, and scouring every inch and cranny of swap mets and junkyards for years to find stuff instead of just opening the catalog and whipping out the credit card!! The only way to get what you want in this hobby is to do it yourself, take your time, roll up your sleeves and stay in it for the long haul!!
I wouldn't deal with the brother of the previous owner, who to me sounds like a jerk to deal with. If he has the cash to buy the car, then sell it to him outright, but I wouldn't take a car back that I didn't want in the first place, especially with a "quickie" job on it. Get the cash and get out of the race car business unless you plan on racing, nobody ever made any money buying and selling race cars!! Just my .02, Geof