There are 2 types of rev. counters RVC and RVI. One senses voltage pulses and the other type current pulses. In my (naive) world there should be no change at all on the rev. counter if you are still using a single ignition coil, because the electronic ignition does nothing else than interrupting the current flow to the coil like the mechanical contact breaker within the distributor would do. Can you provide additional info regarding the electronic ignition and rev. counter ? Maybe these links may help

https://spiyda.com/tachometer-wiring
https://www.gomog.com/allmorgan/smithsclassic.html