Duffman , I have been running a ZX ignition in my '73 since 2001 with the 240 tach and no problems .

Listen to all above. Keep the round top carbs. They can be worked with real easy. IMO they are far more user friendly to troubleshoot than a FI system. True, I still don't understand the FI system completely. Use the ZX dizzy and 5 speed. Note! Make sure you have everything you need to mount the mechanical fuel pump on the head. Pop the valve covers off both heads, You will see what I'm trying to say. I'm pretty sure you will need the piece that works the fuel pump. After that is done and the carbs are synced, have a blast!