Look it over for rust really well. They're not called rustangs for nothing. My cousin is restoring a 67 for a guy and 75% of the car has been replaced. No it's not a shelby, just a 289 4spd car... No it has no sentimental value... Just wants a muscle car and he thought it was really clean... He paid 7k for it too...
I havn't really found any sites like this for the mustangs, not that I looked too hard. I used to like the 65-66 cars, but I've driven a few and they don't do it for me. I do like the Fox body cars.
As for old 302's... They're a dime a dozen. They were fords belly button motor, everything got them. For $3200 you can get a new 345hp 302 from Ford (FMS-M-6007-XB3). Rebuilders have them as low as $1200 for basic engines. Look for the HO roller motors (87-95 mustangs). Cores go for around $400. I've got 153k on mine and it runs strong. Also remember that they changed the balance around 82 from 28oz to 50oz, so balancers and flywheels changed and must match the crank. Also install an HO or 5.8 (351) type cam. It uses the better firing order. The old one beat up the bottom end.
Hope this helps.
David