obviously arches on the back, get underneath and poke the sills behind the kit.
Check the front wings, if they are ford stamped with sealer intact, it means genuine wings still.
the engine are good and strong, and only really go wrong if not running properly (undefuelling is the main killer)

Check for blue smoke on start up, if its rebuilt, there shouldnt be any, a bit on full power and overrun is acceptable, especially if its not standard.

rear chassis legs near the springs are a prime place for rot too.