Thanks for the tips I changed the steering lock today. I did find however that it is necessary to remove the steering wheel on my model which is an 87 - pre Taxi style dash in the UK at least. I think US cars had this dash 86+. It's necessary to remove the steering wheel so you can remove the column cowling behind the wheel otherwise it's impossible to access the clamp nut.
A little trick for removing the steering wheel is to turn the wheels as far left as possible and use an extension bar on the end of a 10mm allen key to loosen the bolt. Turn the wheel the opposite way before tightening.