First you need to decide what type of theft is most likely.
If I was going to steal my truck it would probably be:
1 - yank the ignition switch out with a slide hammer, turn the ignition and start it up
2 - Use a tow truck to raise the rear wheels and pull it away
3 - use a flatbed tow truck to winch the entire truck up and tow it away
For option one there are quite a few alternatives to disable fuel or ignition, or lock the steering wheel. If they decide to use options 2 or 3, all you can do is try to park so that they do not have access to drive the tow truck. That may be difficult if you just park the truck on the street.
Ignition kill switches are relatively simple to install. Some disable only the starting capability (you must push a switch while starting), while others are a toggle that has to be turned on all the time when the engine is running.
You can also get electric fuel valves that have to be activated with a toggle. so you can shut off fuel to the carburetor. One small advantage of these is that the thief may get the truck started using the fuel in the float bowls, but then it will stall at the first intersection when the carburetor runs dry. Most of the time they will not want to hang around to try to figure out why it quit, so the truck will be abandoned a short way from your house.
Bruce