Ok, got the answer talking to a speedo shop. You pop the needles off and then there are little collars under the needles that you carefully pry off. Then the plastic overlay comes out.
For those wondering, no, there aren't any serviceable parts inside. One pcb with everything on it. The reason I took it apart is that the clear "window" of the overlay sheet doesn't line up properly with the alphanumeric display, so it looks very cheesy. I thought they may have been mis-assembled and I could adjust them a bit.
In fact, there was no mis-assembly, very little slack and no room for adjustment. Apparently the misalignment is just part tolerances. In other words, poor quality.
If you have this problem, don't bother. Just get another cluster.