I bought some original Hyundai coil packs assemblies (MOBIS parts) and they come with a brand new tacho interface module.
Ebay currently has lots on offer - For 1992-1995 Hyundai Elantra Ignition Coil SMP 16375YB 1994 1993
This was the 1990 type tacho interface needed to get the early type ignition pulses up a white wire to the cluster - 1990 DSM or 1989 4g61t, but also anything that used the 90 style wiring and had the 4g6x DOHC motor likely. Later it changed to being sourced from the PTU to the cluster and was in a different signal IIRC. Don't quote me, but that is what comes to mind.
I would have to check on the bottom of the coil pack I was using, to see what filter is applied to the ignition as there is one screwed to the base plate.