hope you went for it.. buells are a blast, especially a tuber frame buell. I have a 99 and love it to death. This is coming from a guy who used to ride an 03 r1. Im more of a back twisty road rider then a highway 150+ rider... so its all in what you want. To me a tube frame buell is like a muscle car, basic and raw.
As far as parts go, any tuber motor will bolt right in. You have you choice of swingarms (old box style, 99+ aluminum, or even a XB if you want to get custom but some weldings involved). The nice thing is, the tuber motors share everything with a sportster as well but make double the hp.
Like the poster above, may XB parts fit or can be made to fit. I have XB wheels, brakes, triples, forks, etc on my X1.
good luck