most steering guards mount to the middle bolt of the steering support arm.. Look on the drivers side of the car to the steering pump, there will be an arm at about 45% to the chasis, a bolt will mount above the chassis, one below, one to the steering box and one to the pan-hard rod. You normally remove the middle one.. In most cases the middle nut will come off no problem. If you are lucky you should be able to get the bolt out. If not find someone with oxy-acetalyene!
On the passenger side there will be an empty tube welded to the bottom of the chassis, the other side connects in here.
Now depending on the design of the guard will dictate where it mounts to next. Put a small trolley jack under the guard, yuo can then use the jack to swing it into place and save your arms whilst you try and pop a bolt through.
I can send yuo a pictuer of my one if it helps (however I used a defender one as they were half the price - I just had to weld a couple of brackets in!)
Matthew