Jeff I had a key switch on my Chevelle than operated the inline fuel pump as well as a pressure switch in the fuel line that cut the ignition if fuel pressure dropped below 4.5 PSI (carb'd) so it would have to be broken into with a butter knife, started with a butter knife, then the carb bowls would drain cutting the ignition.

Not like the fuel and ignition systems are the same but some of the same ideas can be used. Add another key switch (mine was small) inline to something....ECM (ground would be sneaky but an easy defeat if found), fuel pump, pink B+ feed to coils....you get the idea.

It's a lot more effective on the cheap than aftermarket BS.

And BTW, it's not easy to defeat the factory stuff out in the open. Think about it....break a window or pry off a door handle in a public parking lot, set up a laptop with licenses to use HPT, etc. to eliminate the anti-theft, break the column and hot wire one all while people are walking about?