Thanks, Derek.

I have since taken a look at an exploded view in the Haynes manual (really nice old style pen and ink illustration I might add) and I see what you're saying. The steering column's worm gear looks as I expected but the driven gear on the pitman arm side looks different than I imagined. I thought that gear would be more of a complete, or nearly complete, circular gear that could be re-centered. But it looks like it's got just enough teeth to provide the necessary pitman arm travel and not much spare travel beyond that.