The shaft is the same and it should work. But why use a castle motor in it when a cheap $19 one from HK will work. It should move very well with this on 2S [link]http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=6527[/link] or this one if you want to get crazy [link]http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=6530[/link]

I run the 2600 in my Widowmaker on 2S and it scoots along pretty good considering it's such and unstable boat. Here is some video. [link]http://www.youtube.com/watch?v=4UkYONC_OhU[/link]

If you go with a 5MM shaft motor you can use the Shockwave BL motor coupler. I think they're like $3 or so.