"Thank you for retrieving this... gentleman for us, Cara Mia. Now, if you'll kindly go to the break room and wait with ATLAS and P-Body, Agent Smith and I need to have a... discussion... with Mr. Freeman."
Well the portal gun and the actual testing facility was established in 1947 as Aperture fixtures then got military permission in 1956 to develop handheld devices. Cave Johnson died in the late 80s so that means that the developments required to merge to two worlds without contaminating the actual portal characters and franchise is quite possible. Bring in the crossover flavor that people are asking for and create a unique early onset of aperture story with cave johnson