Update: I was able to squeeze behind my instrument cluster and feel around and sure enough the speedometer cable was not hooked up at all. It must have sprung out as I was struggling to get the cluster back in place.
I ended up lowering the steering wheel and undoing the six screws so I could pull it away and get it back in place. But it still doesn't work
I suspect I missed a step. All I did was feed the cable as far into the back of the speedometer as possible and then clip the plastic clip on.
There must be more to it than that though since it's not working still.