My suggestion would be to run an electric fuel pump mounted somewhere inaccessible with a kill switch. or relocate your start solenoid. The problem with fords because of the easy access to the solenoid and using a mechanical fuel pump is they are super simple to hotwire. One jumper wire from the pos terminal on the battery to the pos side of the coil then a touch of a screwdriver to the solenoid and Bing Bang Boom you got yourself a mustang. You might make it difficult to enter the car too - remote locks or alarm system?
I am locating my Battery in the trunk, it would be as simple as running an inline cut-out switch and hiding it under the seat/dash. just buy long enough wire for your positive battery wire to run into the car, install your switch where you want it, and run it back out to the solenoid. a bit of a pain for you, yes, but im installing an EFI motor and all that, getting rid of the key ignition, going to flip switch, getting rid of the door handles all that good stuff, so a hidden killswitch is needed in my case just in case someone figures out how to pop my doors. (my doors are remote pop but you can never be too safe)
*EDIT
you could also probably run a cut out from the ignition coil. using the same method.
that way youd hear your engine rolling over and go kick the crap out of whoever is trying to steal your pony