yeah, it was a Harley Davidson engine...Love the 636, the '03-'04 was a much more raw bike then the '05-'06.
Never been a fan of the Buell, I could never get over the fact that they raced the 900 and 1200 in the 600 class and would get killed by all the Jap bikes with half the cc's.
Yours did look super clean though.
gobs of torque, but no top end......
the one I bought had 1700 original miles and was immaculate...
I sold it with 2800 miles for what I bought it for and bought my Yamaha Raider with it...