The early Spit IX's had an enlarged intake to allow for the higher power of the new Merlins. Although having a larger frontal area, these were still quite short, superficially similar to the earlier Mk.V style.
As Squire says, later Mk.IX's (and all Mk.VIII's) were fitted with an elongated carburettor intake containing the Vokes Aero-Vee filter. This was a neat little installation compared with the early (bulky) Vokes filters mounted on Mediterranean Mk.V's, and the smaller 'Aboukir' filters, also found on Med Mk.V's and (early) IX's.
Replicant, I'm down Bath way.
cheers,
Salem
[edit]
As an afterthought, the long filter isn't really correct for the AH Spit IX either. As I understand it, AH models the early Spit IX with the Merlin 61. The later Spit IX's had a significantly better performance. So...new art...or a better Spit.