Sounds like you have the 7 speed FH R-050?  Nice hub but the freehub bodies are not interchangeable
I think they also made an 8 speed version FH R-080  AKA "LX Silent Clutch."
There's a million of the R-050's out there, I know Trek was using em.  Dunno how hard it is to get your hands on the 8 speed version.  Wouldn't mind having one ... it is kinda cool sneaking up on people