How reliable is a '87-'89 Ford Mustang 5.0?
It is old and it was considered a bit of a speed car so it is highly likely that it has been driven hard at some point, but the care is the biggest piece. If it has been maintained well it could last forever. It it has bee ragged on and left to rot it will need a lot of work. Find a good solid one, preferably from a mature owner who knows what has been done and has good records for the car. As with any old car, things will break eventually, but parts are plentiful for those cars.