'81 Camaro steering column removal

I have an '81 Camaro and I'm changing the steering column out because the last people lost the key and broke the column. What's the best way to remove the column from the steering box? It seems to be riveted to the steering box. Before it gets to that there's a spline with teeth, shaft, and U clamp. Is it possible to take it apart there? I took the clamp off, but can't get it apart. Anybody have any good ideas? And when I finally get the column off, how hard will it be to put the new column on?
Thanks!