Couple of other things you can do with old cars are to remove the distributor rotor and remove the wire from the coil to the distributor (sometimes it's just spade terminals on both ends anyway). Just make sure you don't lose them!
Or alternatively, you can also have dummy-wires. Say you have a random wire coming out of the loom, it's taped into the loom and everything, but isn't connected to anything. Plug that into say the coil, and tuck the real coil wire out of sight (or plug it into a relay or something nearby that's also a decoy). On a visual inspection, everything will look copecetic but it won't start.
It won't stop anyone really determined to get your car, but it will probably foil the opportunistic thief that isn't familiar with old cars
clever, long term thing to do.
of course, one could haul it off pretending to be a tow company.
if thereis a chnce to take and someone wants.. they will get even if it is a short time (law will catch up)
the other night I put fuel in the car while running, walked away from it for the store... a subaru 20 years newer than mine shows up, lady points the key at it to get the blinking lights and little horn to verify an alarm.
both old and new at the same place.
I still can't even do airbags with a comfortable thought...the alarm stuff is just as anti-faithed as the police shooting for wrong reasons.
I walk down the middle of it.