Consider this: you've seen all those people rushing to stop the guy who's opening the car with the alarm sounding?

Neither have I.

The alarms will keep honest folks away, but that's not the work. Something like Lojack or OnStar, with the tracking capability, is the best option. Everyone just growls and ignores the sounding alarm - "damned yuppies and their car alarms..." - but something that immobilizes the car (fuel cutoff, similar), and that tracks it if it's trailered and moved, works well.

For the car shows and so on, if I'm not there to enforce the "don't touch" signs, I like the alarms that detect movement, so if someone leans against the car or otherwise tampers with it, the alarm sounds. That's one place where folks pay attention to the alarms.

You're dealing with a car that shares most of the body platform with mine, but you don't say what you're using it for. On another '69 Shelby, I had electric fuel pumps and a hidden switch. If you got it started, you only went as far as the fuel in the carb would take you. But that was 20 years ago. As you can guess, my car doesn't get left unattended much. But if Lojack comes to my area, I'll add it.

As far as the alarm, if you're going to show the car, get one that has the sensors (proximity, movement), and set them to be appropriately sensitive. You can hide the siren under the front fender by removing it from the car and running the wire through the firewall. If the alarm is behind the splash shield, it won't show when judges are looking at it. While you want the flashing LED for notice if the car is sitting out in front of Outback Steak House, you don't want it visible for a Thoroughbred class show car. Be appropriate.

Many of the better new alarms will include an ignition kill that will work with the old, non-computer cars. Slick stuff like remote start won't work - requires fuel injection.

Best thing is to remember that no security system will keep your car 100% safe. My car is stored in a garage with an infrared motion detection alarm, connected to call via cellular service to an alarm company. Fine. If someone wants my car, they may well have it out of the garage and on a transporter before the sheriff arrives.

Tracking is my #1 choice, followed by something to disable the car. Audible alarms make you feel good, but are of limited help. Just my nickel's worth.