I am a bit confused. First you asked about stacking on the same tower and then you say you will be using two different towers? Is that right? If so you will have no problem with interaction especially if they are not at the exact same height. When stacking different bands on the same tower you can put smaller antennas like 2m yagis in between larger antennas like tribanders without that much of an issue. I have to do this on my mast as I have only about 17 feet of mast above the top of the tower but have six antennas to mount. All antennas will be horizontal except the 2m FM antenna.My installation will have an Explorer 14 at 62',an A147-11 at 64' mounted vertically, an A3WS at 66',a 13B2 at 68', a homebrew six element 6m yagi at 73' and another phased 13B2 at 78'. I expect there to be some interaction however by all accounts the spacings I have chosen based on my available mast length should minimize this. In the past i have had the 6m yagi mounted a few feet above an A3 tribander and a 2m yagi about five feet above that and saw very little if any problems.