This is the tach and pod:

It's a normal, standard tach that needs a typical ignition-based signal, and I came across a company called Dakota Digital that makes a simple little box that tells the tach what to do with itself
http://www.dakotadigital.com/index.cfm/ ... prd129.htm

It operates via two ways, and the one I opted for was by the simple method of counting flywheel teeth. Tell it how many teeth are on your flywheel, set the module accordingly, supply power and ground etc etc, and the nice little mini tach reads just like its plugged into a coil.
The DSL-2 kit comes with the DSL-1D module and a simple magnetic pulse sensor, and all you have to do is mount the sensor somewhere where it can 'read' the flywheel teeth accurately - I chose the tranny inspection cover.

In order for the sensor to be 'square' with the flywheel I needed to modify the cover - I cut out a square 1.5" section and replaced it with a flat version of itself relative to the flywheel, but also up on the side a bit to avoid excess oil and water drainoff. First I needed to know exactly where the flywheel was and how close to the cover it was -

Cut the cover, install the 'shelf', and it looks like this -


Drill a hole just shy of 3/4" and install the sensor. I used clay to measure the distance between the sensor face and the flywheel - I opted for 1/16" - not sure what it's supposed to be but it works great.
As best I can tell it's dead accurate. You can adjust it based on how many flywheel teeth there are...and that's it. The kit cost ~ $110, and it was a simple install. And with it you can use any tachometer on the market you can find.
- M2