speedometer not working - how to remove cable?

My speedometer on my 86 Monte Carlo SS isn't working. I feel it could be a faulty speedometer cable. Should I remove the entire guage cluster from the dash to get access to it, or do I remove the speedometer only? And if so, how?

Also this green module is unplugged, and it has a black / red black / green wires going from it to the speedo - could this cause the speedo not to function? I believe it is a Speed Sensor Cruise Control Buffer used to tell the ECM the vehicle speed for cruise control, however the car has been LS swapped with an LS PCM so do I even need this?

Finally, if I upgrade the bulbs to LED, should I still look to paint the back of the cluster bezel white to make it more reflective? Or is that not needed with LEDs? The current setup is extremely dim.

I managed to remove the cluster and change out the speedo cable, and the speedometer is working now. However it is jumpy. The cable I am using is from Amazon and is a foot longer than the one that was there - will too long of a cable cause problems?

Also noticed that the trip meter can't be reset with the button and it seems frozen?

The drive gear is unknown in the tail housing, I am thinking I should remove the speedo cable and the retainer clip around it on the tail shaft to peek and see the color of the gear before deciding if I have the right one or not - I am certain it is wrong because in my short drive at low speed, the car was reading higher mph.

Do I need to reinstall the green speedo cruise control sensor box if I have an LS swap and no factory ECM anymore?

As I am trying to swap LED bulbs, I noticed a couple of the 168 bases are crumbling as I turn them, I think I will get new bases. Some of the bulb sockets aren't working even with new LEDs.

Some bases are blue, some are green, two are white (flashers), one is black (MIL I believe). Is there any electrical significance to these colors?

I also noticed the cluster with the circuit ribbon is stamped 1981 where as a lot of other plastic pieces in the car are stamped 1986 (the year of the car). Is it possible that the cluster circuit is from an older 1981 car?

I tried to clean every contact with contact cleaner and a paper towel.