Nice Job!
We use the same emitter/detectors to do timing on our slotcar tracks. I have found that the emitters that Radio Shack sells seperately have a higher output rating and work better with 2"-3" seperation that we use on the track.
I have thought about doing an optical coin door a couple of times.
I don't have a coindoor, and I might never have one, but if I did, it would be optical.