I'm sure you already know this stuff... Remove the steering wheel and turn signal switch.
With the key in the run position, there is a small cylinder pin along the lock cylinder housing towards the right outside edge, this can be pushed in (or...down), but only with the key in the run position. Once that pin is depressed, you can withdraw the cylinder from the housing collar (again, only with the key in the run position).
If the pin is jammed up from something the thieves did to it, you can drill it out and then withdraw the cylinder with the key in the run position, just be sure to clean out any debris from the cylinder's bore once it's out.
Worst case scenario, you have to replace the entire steering column collar that houses the cylinder. I had to do that with my 78 Sedan when one of my ex's messed up the cylinder to the point it wouldn't turn AT ALL. Color matching the interior paint so it still looks original is the hard part.