I'm about to have a similar "problem" to this with an antenna Azumith/Elevation (Az/El) rotator. My Az needs almost 360 degrees rotation (it has a South "stop" so the cables don't wrap around) and the El needs 180 degrees. My thoughts were heading towards using a compass sensor such as the HMC6352 http://www.sparkfun.com/products/7915
for the Az so I knew where the stepper was but I was having trouble finding an inclinometer to handle the El stepper motor. I was trying to stay away from the mechanics of using a pot with such a large rotation.
I like the look of those opto slot switches, should have thought of those sooner - thanks for the tip