The fact is that these cars are very easy to steal. I lost my keys to my '68 when I was in college ('72) and it took me less than five minutes to hotwire and take my car. I found some scraps of telephone wire left around some constuction and jumped the battery to the coil. Then I coasted the car to start it. If the car had been an automatic, it may have taken an extra minute or two.

One thing you can do to help is to run a hidden switch from the points side of the coil to ground. If the points never open, the engine won't run.

Back in '72 I had to leave my keys in the car at some of the parking garages so they could move the car so others could be let out. I put in a thermal time delay switch that let them run the car for three minuts and then killed the ignition. Amperite made these. It was a 12 volt heater and bimetal all inside a glass bulb. I forgot to turn it off a few times and would get three minutes away when it kicked in. I got the idea from my uncle who's Tempest was stolen but found a few blocks away because it would always stall out for the first ten minutes. Thieves don't stick around a stalled out car. They may stick around tinkering on one for a while in order to start it.

With some of the electronic ignition kits it would be easier to conceal a kill switch.

Another way would be if you have installed an electric fuel pump, to add a hidden fuel pump switch somewhere.

As someone here said, if they want your car badly enough it's gone. A friend woke up at 3AM to see a tow truck backing up to his Grand AM. If he had not wakened and turned on the outdoor lighting, it would have vanished. You can only make it more difficult to steal, not impossible.