Nagaro:
- can i mount both ir sensors together to build a break beam sensor (like the picture from dougp) ?
That exact configuration probably will not work. You need to know whether the sensors are modulated. If they are, each sensor is looking for its own light beam and others will be out of sync. You could try a corner cube reflector and a single sensor to make a retro-reflective sensor but I believe you'd have more success - and less fuss - using something made for the purpose. You might have to do some level translation but the sensor will be reliable.
Don't forget, you have to come up with a way to mount whatever you decide on. Commercial offerings are amenable to a wide variety of mounting options.