I require a 4-cyl tacho to install in place of the OEM unit in my Cressida, as the existing unit will read incorrectly if we wire it up...the reason being that, as part of the after-market wiring solution, we used two 4-cyl ignitors (1 for each bank), and we need to take the tacho signal from one of these ignitors...
I'd guess that an SV21 Camry (non-V6) would do the job, or something similar.