I vaguely recall that there is a thread on this somewhere in the distant past, but I can't find it. But in looking at pictures of control cavities, the filter in a series instrument does appear to be a different part than the filter in a non-series instrument; and the series filter is physically bigger. Again, I vaguely recall there being a thread that explains why the series filter is physically bigger, but I can't recall why, and I can't find the thread.
On the question of whether the frequency range of the filters is different for guitars than for basses, I found this comment by Mica posted in 2008 ...
"The filter range is the same on Series I and II basses and guitars. The Activators do have a higher filter frequency range for the guitar filter, but there's no reason you can't use an Activator bass filter on a guitar.
"My dad has been wondering lately if we shouldn't make all the filters bass filter range."