Your E-7 will run a dual elevator system without a problem, it just can not do it on separate channels. You will either have to get a servo reversing Y harness, or a reversed servo. I prefer the latter as reversing Y harnesses can sometimes be a source of difficulty. JR sells reversed servos for some applications. I have Hitec service reverse mine for me and the cost is quite reasonable. I can not advise further on Futaba or Airtronics. It really is easy to do yourself, but for the few dollars that Hitec service charges me it does not effect the warranty. To me that is worth the cost.