The first thing is to make sure that you have two healthy birds on your hands. The rescue that you have taken in, did you quarantine it and/or have it vet checked before housing it in the same room as your Grey? With rescues especially it can be very hard to put faith in the fact that the bird is healthy, since you really cannot gauge much of its history before coming to live with you. If you have not had the amazon checked by your vet that is the first step before thinking about introducing it to your grey. (And at least a 90 day quarantine if you have not done so already. Although, if you have had the two guys living in the same room since you brought the amazon home then it may be a little late for that.)
I have successfully introduced both of my amazons together as well as my conures. With my amazons it was a matter of pushing their playstands closer and closer together until they were touching. The key is to give the birds enough room to back away from each other if they decide that they do not like one another. My conures are flighted and introduced each other themselves, my sun was out playing and my GCC decided he wanted to go say hi. Not intended, but it worked. They had been living side by side in my birdroom for several months before the introduction, and often would sit on perches nearest to each other in their cage, so I had a feeling they would be okay before the introduction ever happened.
The biggest concern is to stay very close by so you can separate them if necessary, watching for any signs of aggression. Your birds may like each other, and they may not- it is a crapshoot. Good luck!