I don't know if anyone mentioned this yet, but the gunslinger could be Mikio Itoo. (Doubt it.) If anyone has mentioned it, can you link the thread to me, because I didn't find any direct posts involving him from a few searches.
Well, I was reading through some of the earlier chapters, and I noticed in on of the SBS's, Volume 4, before chapter 33, that there was a mention about Mikio Itoo. He was a quick-draw expert and Oda said we'd be seeing him again soon, or something to that effect. From what I recall, we haven't seen him yet, so this would be a great time to bring him around, 9 years is a long soon. This theory is very farfetched and most likely wrong, but I thought that I should see what you guys think about it.
Again, if this post is completely and utterly useless, sorry about the trouble.