^^^ Nice Bronco II. I can understand why you'd want "harden" it against theft.
A hidden kill switch is a good idea, and there's several ways to do it, all fine.
In my opinion, the first best deterrent is a flashing LED, mounted where it's easily visible. These are part of most every alarm or immobilizer system, and one can be configured alone in several different ways (through a switch, as part of a kill switch install, or even automatic when the key is off). Current draw is not an issue if the vehicle is driven regularly.
"Deterrence" is what you're looking for. A hidden kill switch may prevent a drive-away theft. but the vehicle may still be damaged in the attempt- smashed window or scratches from entry, and a busted column and ignition switch from the hot wire attempt.
A blinking light gives you a better chance that a thief will pass up your ride, for a target without such an indicator light. The thief doesn't know if it's a dummy light, or if the vehicle has an alarm or owner-paging system.
It can also deter "smash and grab" content theft.
I think that you're on the right track, in doing something to help protect such a nice truck.