First of all, you need to decide what kind of ending you are going to create. What are you going to have happen, instead of the ending that exists. Once you do, try creating a sort of outline for that ending; a brief statement of what is going to happen, and in what order.
Secondly, if you look through the text of the story, it is notable that Poe often uses quite long sentences, filled with semi-colons, dashes and commas. ("Such a supposition, notwithstanding what we read in fiction, is altogether inconsistent with real existence;—but where and in what state was I?") So no matter what words you do use, try to frame them in longer, more complicated sentences. You can try this by writing it in your own words first, and then merging sentences using semi-colons, and trying to add dashes and commas after that.
As for his word choice, keep in mind that this was written 150 years ago; Poe's word choices are going to be much different than the average person today. They will be more elevated and "fancy" sounding. One way around this is to write a sentence then use a thesaurus to "fancify" some of the word choices. Just be careful to not use really strange words, or words that completely change the meaning of the sentence. The other way is to read through the text, and highlight repeated words that you find, then try to work those into your ending.
These are just a few ideas to get you started; good luck!