Removing the two screws was a good idea. The centre boss is keyed. I swapped my original yoke with a better one some time ago. I can try and refresh myself this weekend. I think the boss/ key way is a diff diameter iirc. You should be able to get the yoke off ok.

Btw Dave, mine will stay as a shack. It has sentimental value coming from a dear friend in London in the 80s. I remember taking it from his home to my digs on the underground. I make take it to Cockpitfest to display