I agree with a lot of the earlier comments - these cars don't get knocked off anywhere near as much as years gone by, simply because they not being left where they can be. A very small proportion get used as daily transport nowadays, where they're most at risk.
Immobilisers and alarms are very straightforward to fit, of course. Just remember that the rear doors never had the switches for the interior light, so if the immobiliser uses that circuit, you need to wire them up.
I like the sound of the solenoid system though - is that a legal line-locker?
There was an
original steering column lock accessory, and NOS ones do still turn up from time to time. They're not easily removed from old steering columns because of the shear bolts used to secure them. Unlike modern steering column locks, these locked the gear-stick in place, not the steering wheel. And of course there is the much more common
sleeve lock, which is quite effective at securing the shifter to the steering wheel, and can only be bypassed with either a hacksaw or by removing/replacing the steering wheel.
I've got a friend who used to leave the steering wheel retaining nut only finger-tight, so he could have the wheel off in about 15 seconds and either put it in the boot or take it with him! He may have been related to Mr Bean...
There also used to be a very cool accessory called "The Joker", that was a key-actuated carby lock. Like kill-switches, sleeve-locks and club-locks, not impossible to by-pass, but enough to frustrate the casual joy-rider.
But like anything else, if someone wants it bad enough, there's very little you can really do.
cheers
RET