I just have 1 satellite rx on my 450 with 3GX but I've two satellites on my 600, for various reasons. But...the antennas on one rx are vertical and the antennas on the other rx are horizontal. One is on one side of the helicopter and the other rx is on the other side.
Since you are talking about a 450 helicopter, I've heard and read that you really only need one but there's no harm in using two satellite rx's. If you can mount one near the front of the helicopter (maybe under or in front of the cyclic servos) and then mount the other rx at the rear, near the tail boom....I'm sure you'll be in great shape.