Get the Boss. GT is a solid car, but the numbers for the 302 are better, and much further down the road that 302 will be worth quite a bit.
While you're at it, snag an SN95 Cobra. They're stupidly cheap right now and sometime later on they may be worth a good chunk of cash. My friend got his 97 Mustang Convertible for 2 grand.
2. Freaking. Thousand. Dollars. That is stupidly cheap, my damn Pontiac Sunfire is worth more than that, and it's a 2001 model.
If he holds onto it like he says he will, that thing might be worth a lot by the time he's 50.