For an everyday driver please consider fitting a good alarm with engine immobiliser, as the 66 Mustang's bonnet is unlocked from the front of the car, rather than by an internal cable.
You'll need an alarm with a battery backup, as the car battery is easily nicked.
The saving grace is that mostly only Mustang people will have this information, but you've still got to protect yourself from that one person who has the knowledge, and is out for mischief.