For quite a while, I used a Master Lock placed right in the hood release slot. Worked fine, couldn't move the hood release lever far enough to release the latch. No chain, just a key needed. All you need to do to disable the car at this point is remove the lead to the ballast resistor and the car will not start. Not as convenient as a hidden switch, but it protects the underhood area as well as prevents theft.
This works for a 1968 Barracuda, but I haven't tried it on a Dart, Duster, or the like.
Bob
