For the speedo; the cable drive has a magnetic element, as it spins it induces a magnetic field in drum to which the needle is fixed causing the needle to move. Unless the magnetic drive to the speedo is re or de-magnetised you can’t alter the amount the needle moves, the speedo will only read correctly at one speed.
Prior to taking your speedo to bits, calibrate the speedo by having a passenger record the shown speed against a GPS device, (satnav or free speedometer App for your phone). By doing this you will see how fast or slow your speedo actually is.
Then pick the speed you wish to the speedo to be accurate at (say 70) and note the speed shown on the speedo (say 85).
When the mechanism is out of the case, manually turn the needle to 85, hold it there and with a fine felt pen put a mark on the magnetically driven drum against a fixed register point on the mechanism.
Release the needle and then pry the needle off the shaft with a couple of tea spoons as levers. Once off, rotate the drum so your mark and register re-aligne, then refix the needle at 70. The speedo will then be accurate at that speed, for the example given the reading will low below that and high above.
You can then remount the mechanism in case without glass, afix the cable drive and repeat the GPS test and readjust if necessary before you button everything up.
And lastly, put the tea spoons back.