with the rpm needle going up and down eratically coupled with a misfire is a sure pointer to the coil end of things or the ignition amplifier,the green wire comming off the coil goes to the rpm clock and so many coil pulses equals so many revolutions,if the coil pulses eratically it will show on the rpm clock and its the ignition amplifier which plays a part in this but doesnt actually tell it when to pulse.but they can give trouble and are an easy fix
another cause can be bad earths on the inlet manifold and elsewhere on the engine,also the 3 big block connectors at the back of the engine bay are also known to be a cause of this problem,have a check of all the engine earths and open and close the block connector a few times to make a good connection and do the same with the ignition amplifier connector