Okay. I know a stock '77 would likely have a Holley gold box electronic ignition. Those are easily damaged from leaving the key in the on position while the engine isn't running. Really, it's not a good idea regardless of the ignition system you have. Hopefully you've been disconnecting the battery anytime the engine isn't running. If not, you really should until you get your key switch problems fixed.
In so far as stopping your engine without the key, keep in mind that it needs an uninterrupted supply of air, fuel, and spark to keep running. So removing any one of the three from the equation will kill it. Cutting the fuel supply isn't practical, but choking off the air supply is, by forcing the choke closed or otherwise smothering the airhorn of the carb. This would be the safest method. You could also pull the main plug-type wire that runs from the coil to the distributor, but be very careful as there is a risk of electric shock involved. You'd make an excellent conductor especially with wet stuff on the ground.
Scout II's utilize the same basic ignition switch and key tumbler components as found in millions of GM vehicles from the same era. The ignition switch is located further down on the steering column and is activated by a plunger rod that runs up inside the column to the key tumbler. To access the ignition switch, you'll need to remove the instrument panel cover and the plastic skirt that wraps around the steering column. Then you should be able to see the switch and the plunger rod and begin to determine why natural movement is being restricted. Either something is frozen up, bent, broken, or way out of adjustment. Removing the ignition switch from the column should allow you to easily turn the key back to the off position. Then you can try wedging a narrow screwdriver or similar into the key release slot and try to force what remains of the broken lever down and rotate the tumbler to the lock position, which is the only position that is supposed to allow the key to be removed. As for fixing the broken lever, that involves pulling the steering wheel and removing all the horn and turn signal switch components. I think your chief concern right now lies with getting the tumbler to actually move freely from off to start to run and back to off again, so that you don't have to play the bothersome stall, smother, or electrocution game.
If it becomes necessary to replace the ignition switch, there are two choices. Making the right one depends on whether you have a tilt or non-tilt column. Be sure to specify at purchase time.
