That freehub body is Hyperglide only, It post dates the Exage Mountain group. Either the previous owner replaced the wheels or the freehub body to get more sprockets and Hyperglide.. Based on the rims, I suspect the latter but we should be able tell which case is correct via the hub date codes, Shimano use to stamp the date code onto the barrel of the hub shell but around this time had transitioned to one of the hub flanges.