Definitely drop the tire pressure. Also wondering what springs may be in the car. The MK1 I built back in 98 used the stock mustang rear springs and coilovers in the front. The old english door latches never really fit tight in the cobra or any of the english sports cars I have owned that used a similar latch. An appropriate use of weatherstrip and rubber bumpers will help to tighten things up or at least decrease the rattle.