punchtape.dxf has the basic mechanical design of the read head. The head is bolted together with M3 hardware.
boards/5mm-phototransistors contains Eagle CAD files for the LED emitter and phototransistor boards.
The reader is implemented as an Arduino sketch in punchtape-reader/punchtape-reader.ino. I'm using a Teensy++ 2.0 at present but it should work with any ordinary Arduino variant. You'll have to alter the pin assignments at the top of the file, though.