Just go get one out of a wrecking yard, or one from someone on here selling a cluster. I wouldn't buy a new one, for the price of new (from LMC) you could probably get 3 or 4 complete clusters from here.
Pulling the needles off is fairly difficult to do without breaking the gauge. Why were you taking it off exactly?
And the post title, how to pull the speedo cable off, you unbolt the instrument panel bezel (big black or aluminum covered piece that goes over the gauge, headlight switch, etc) unbolt the cluster housing (blue-ish piece) either pull it towards you or move it so it WILL come towards you, and feed some speedometer cable through the firewall from the engine bay, then back inside the truck, reach behind the cluster, follow the cable to where it hits the back of the speedo and pull the spring steel tab (on the "top" of the cable/speedometer as it's mounted) towards you, pulling the cluster housing as well. Will still be wires and what not connected, but if you JUST want to get the speedo out, now you can by unbolting all the stuff in the front.
Since you have VSS bolted to the back of your speedometer, I don't believe you can feed enough speedometer cable through the cluster without actually unbolting the cluster from the dash. You could try, but I think the VSS wires are too short.