I recently installed a 2JZGE VVT-I engine into my Hiace SBV running off a Microtech. The standard Tacho was obviously reading 50% more than it should. My local instrument guy said he could not reconfigure this Tacho as it was a late model and works off a square wave/digital signal.
I found a mob in the States that builds a module that does this conversion. It was a simple hook up with 4 wires (took 10 minutes) and presto Tacho reads correct.
It was $175US plus postage, which was cheaper than the instument guy.
The site is www.momentummotorparts.com