Very cool
You'll definitely need to test it before installation to make sure that your R2 value is good. Do you have a spare battery around or maybe a 14.4 V rechargeable battery for a power tool?
Spare cigarette lighter adapter that you can splice the wires into?
I suppose you could always test it in the car before reinstalling it completely.
To set the emitter and detector, I used hot glue. You can then warm the glue after it has set with a heat gun or similar to move and aim them better if necessary.
Edit: if you used the IR emitter and detector that I linked, as well as the resistor values, then you should be fine.