prototype an opencv stereo vision test

My company is doing Escape Game props. I do electronics (industrial level, coming from kiosk industry.. no arduino here), mechanics and software. I am checking into having new features that are related to player position. Idea is to get the position of the head in space when user is looking into a device. "in space" means that the user (single, centered and mostly fitting the whole fov but might also have other faces in view) is located around 40 cm from both cameras. Position needs to be pretty precise (mm range on X/Y, cm Z). IR cameras will be synched, calibrated videos will be sent to dev. No hardware is needed as you'll work from videos. Calibration files would be sent too. I expect two Harr to detect eyes on each of the camera frames and then some maths to indicate spacial position of each eye. If an other method can extract eyes with better probability or position precision, dev can submit proposal. Speed is an important factor in order to avoid lag so no "multisecond on a PC" solution would be taken in account. Language: C/java/python possible.