How many pickups depends on what you mount the sensor on. I have a better solution though.

You need one of these.....

http://www.glowplugsdirect.com/index...dkv6drd9vf4642


Fit that in the gearbox speedo cable hole and wire it up. It has 3 wires, one earth, one ign live and the other goes to the stack. I have the wiring and settings somewhere too but may take a while to dig out. (or give Martin Hadland a ring as he told me about it)