If it's a factory V8 car and any of the mounts are still there, it won't be too bad. You'll need an original oil pan for the 302, although I've heard stories of large hammers and pipes being used to "modify" a standard pan. With the original cast exhaust manifolds, any of the small bellhousing C4 automatics will go in. If you plan to use headers, you'll need the original Mustang II bellhousing/flexplate/convertor.
Most of the parts used on the II for v8 installation were specific to the car....a donor car is a Godsend.