Yes, it is the 14K resister that you will need to find the parallel equivalent for. Have you studied how to calculate parallel resistance yet? Two, 9K resistors in parallel will give only 4.5K.
The formula using two resistors, R1 and R2, to get the resistor you need (Rn) is:
Rn = R1*R2/(R1 + R2)
Edit: I don't know what data you are talking about including in the IR transmitter signal. I think you may have confused the three different uses for these devices: 1) beam break detection; 2) data transmission, as in a TV remote; and 3) proximity detection. You are doing #3, I think. Also, at the outset, I thought you wanted to use 555's for the transmitter and an MCU (16F877) for the detector. You can also use an MCU for the transmitter.
Most important is for you to set out what you want to do in a logical sequence and work on getting that done. It is easy to get pulled in different and interesting directions and to want to try all sorts of new ideas, but that will really lengthen the time it takes to get to the finish line. I think the simple transmitter design I gave you will work. I would spend my time on prototyping it to be sure it works and then concentrate on the detection and analysis of results. Once you get the programming under your belt, if there is time, you can return to improving the transmitter.
John