[updated:LAST EDITED ON 01-12-03 AT 05:14 PM (EST)]I got to it by reaching around the guage cluster itself. As you have found, there is no way to reach it coming up from the bottom. Unplug the electric harnesses on the back of the cluster itslef, and see if that gives you some slack to pull out the cluster enough to reach behind it and unplug the speedo cable.

Edit: the guage panel should be loose, and should come out with the plastic cover on it. I noticed in your picture that the plastic cover is off, and wondered if you just got that off and not the entire cluster. Just another thought, I'm not trying to insult you in any way, I'm just thinking of more possibilities.