I was able to source the tach module from my donor car, but I thought I'd post some more useful info. I've used this to recalibrate multiple tachs in various swap projects I've done.
His article is very good, but I thought I'd post some info to make it a little more easy/scientific
Instead of using the car itself to calibrate (free revving etc) you can use an EL CHEAPO battery charger as your signal source. Basically you need to power up the guage and ground it with a 12v power source, like say a PC power supply.
Then on the signal input you use the battery charger, here is a snip from the place I learned how to do this:
Quote:
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PREFERRED SIGNAL SOURCE...an inexpensive 12v battery charger can be used as a deadly accurate signal source for the re-cal of your tach. This signal source is so steady and accurate that there is no need to compare the reading with another V-8 calibrated tach. Battery chargers typically use a rectifier bridge to convert the AC power source into DC. This turns the 60 hertz sine wave input into a 120 hertz ripple wave DC output. The ripple wave output is be read as 3600rpm by the stock rotary calibrated RX-7 tach. For a V-6 application, an RX-7 tach should be adjusted to read this signal as 2400rpm. For a V-8 application, adjust your RX-7 tach to read this ripple signal as 1800rpm. Please note that you must use a 12v battery for a power source, and the battery charger as a signal source only. The ground wires for both the battery and the battery charger should be connected to the ground terminal of the tach.
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I realize that says RX7, but the RX7 tach works like a 4cyl tach. So the RPM values are still valid. The cheaper the battery charger the better, some of the baller models don't behave in this manor.
I've used this method on two RX7's, my S10 and a Mustang.
Edit:
http://members.tripod.com/~grannys/rx7tachrecal.html
Gotta give credit, where credit is due