Crank position sensor

[ST3XD at Jetson.UH.EDU]

Assuming we will hammer out the controller, the first and most basic
sensor we need is the crank position sensor.  If we are going to make
a true SEFI system with distributorless ignition, a highly accurate
crank position sensor is a must.

But how?

I've seen some setups using magnets, but how can these be installed?
Do holes need to be drilled in the harmonic balancer with little 
magnets placed in them?  That's the only way I can come up with.
The racing setups are great, but we have to install this on our
engine with minimal (hopefully) modification.