[Formerly Steve Wilkinson]

Funny, I just did this yesterday. I actually removed the electrical cassette from the lock part without removing the entire assembly from the steering wheel. I couldn't get the headless bolts out even with a strong screw extractor and felt that grinding the heads off wouldn't do much good because then I'd still have to drill out and re-tap the bolt holes, which seemed like an enormous pain.

So I got all the under-panel wiring out of the way by unplugging it from the four sockets on the bulkhead, then easily got the bottom screw out of the electrical unit. The top screw was a bigger challenge, since there's limited room. I cut a narrow-barrel metal jeweler's screwdriver to a length just long enough to protrude a half inch or so beyond the electrical unit, so I could clamp it into a small Vice-Grip. If you remove the hazard-flasher barrel, you can actually see enough of the electrical unit (with the help of a flashlight, of course) to maneuver the screwdriver into the top screw, then once you can turn it just enough to loosen it, it can easily be spun out by hand the rest of the way.

That's no help to you, of course, since you already have the troublesome headless bolts free, but I recount the procedure simply to tell people that the common wisdom, perpetuated in Wayne's excellent book--"It's impossible to do with the ignition/wheel-lock unit in place"--is not true. (Actually, Wayne writes that a few mechanics have told him it is possible, but he's doubtful. I'm not a mechanic, but I do play one on teevee.)

Anyway, as for your problem, page 213 of Wayne's book shows not "a screw" holding the lock onto the steering wheel (photo at top left of the page) but a substantial nut and bolt. Loosen--do NOT remove--that nut and your assembly will slide out.