You will need to mount them looking at the floor. Our team made a simple plate out of Polycarbonate to mount them.
Simply drill 3/4 inch holes to fasten the photo-sensor, and you are good to go!
You might also want to check out this line following tutorial:
http://decibel.ni.com/content/docs/DOC-14730
And this Datasheet
http://www.ab.com/sensors/photoelect...eral/42ef.html