Tim - I fitted mine using rivnuts into the chassis.
On one end of the bars you'll see an angled foot which conforms to the chassis where it tapers back over the suspension arms. I aligned the front edge of that foot with the weld line where it begins to taper.
Then it's just a case of deciding how high up you want them, and then getting it level before marking up and drilling holes. I believe mine are just below the door sill. Obviously they need to be hight enough to clear the rubber mounting bobbin the exhaust hangs from.
Once you have it looking good on one side, wash rinse and repeat for the other.
