Did you loosen the three bolts on the firewall that hold the column plate to the firewall?
There is also a bolt near the rear of the column, that bolts to the pedal assembly bracket.
Getting to the speedometer cable on an A-body would try the patience of Job.
And, it helps if you're a contortionist with small hands.
You've got to lay on your back with your head toward the firewall and reach up through the brace behind the instrument cluster to reach the speedometer cable.
There is a small hook on the side of the cable that holds it to the speedometer. You've got to squeeze that clip and pull the cable out.
Good luck. And, keep some bandages handy. There are a lot of sharp edges under the dash that will cut you. DAMHIK