If someone already knows this, or is actually capable of opening the vault and having a look at original drafts, notes and/or storyboards is Lucasfilm's Pablo Hidalgo ( twitter.com/infinata ). It wouldn't hurt to ask him via Twitter I suppose. If a bunch of people ask the same question, he might just take the time to research and give an answer if he doesn't know for sure already.
FWIW, I always thought that tower belonged to a regular SD, not the Executor.