'i'm not a specialist in Weber Marelli managements (I favor MegaSquirt if you havent noticed ), and don't know how to convert one to wasted spark. But, if you manage to do so, then you can drive the rev-counter from the coils using three diodes like this:


In ford's efi managements one can just take pin 11 form the EDIS-4 to drive the rev-counter. Most people seem to change the entire instrument panel for no reason.