First of all, Mark, I was just going to say that I don't anticipate ever doing a story that would fit into the details of your question. I won't be writing any fictionalized and fantasticalized account of an historical figure. But then I recall I did exactly that when I wrote Robert Louis Stevenson into my second Beowulf novella (or was it a novelette? I keep forgetting the official divisions), even going so far as to make him the villain. That was the textbook definition of taking gross liberties with the facts. In that case I read the widely available details of RLS's life, found out when he was in America, when he might possibly have been wandering about in the old west, realized that I would have to fudge the dates by a month or two, to make it tie in with the rest of the book, and with malice aforethought went ahead and did it, changing what I needed to change to make the story work.
I think that's an entirely legitimate way to do it. Then again, once I was willing to take the arguably outrageous step of making RLS a villain -- for which there is absolutely zero supporting evidence -- rearranging some of the details of his actual timeline by a month or two didn't add much to my sins.
But I do sort of have a personal policy of setting the record straight in the afterward notes, when I do take such liberties. I call this the Bernard Cornwell rule, after the author of the wonderful (you need to read these) Sharpe's Novels, wherein he takes sometimes huge liberties with the facts and events of the Napoleonic Wars, so as to properly insert his fictional hero into every major battle, but then carefully explains the changes he made by providing an Historical Note at the end of each novel.
Another example: In Peter and Max I had to move the dates of Hamelin's main Pied Piper festival, in order to make the fictional timeline of the novel work. I had no trouble doing so, but I did mention it in the back-of-the-book material.
That's my personal rule, but I don't necessarily believe it should be a universal rule. I probably believe -- I say 'probably' because I haven't yet given the matter all that much thought before now -- that a writer of fiction should be free to take just about any liberty with the facts, the history, and the public record (not always the same things, but you already knew that) for the good of his story. It's called fiction for a reason. And, he should not be required or even expected to explain himself. Many are of the mind that a story should always stand on its own, not needing an explanation or apology at the end. I don't know that I absolutely subscribe to that notion, but I can absolutely see the sense of it.
I would encourage you to take any and all liberties with Tom Sharkey that you deem necessary to your tale. And I agree with Bill Williams that, if a Tom Sharkey biography ever is written, you're likely to be the one to do it, and thus will have plenty of opportunity to set the record straight.