We used these last year. They run off of 5V instead of the 5 and 12 that the FIRST sensor boards needed. They are open collector so you have use a 4.7K pullup resistor on the output signal.
http://rocky.digikey.com/scripts/Pro...480&M=1GT101DC
Here's a thread with pictures on how they can be mounted:
http://www.chiefdelphi.com/forums/sh...ad.php?t=62083