Ok, unless I am quite mistaken the Mk 8 could be assembled from the 3D parts of the other Spitfires.
Take a the tail of the Mk 16 to use as the tail of the Mk 8 (Mk 14 has an enlarged rudder compared to the Mk 8 as I recall).
Take the fuselage of the Mk 14 from immediately in front of the cockpit to the tail, including the retractable tail wheel.
Take the universal wing of the Mk 9 with the exception that you take the shorter ailerons from the Mk 14.
Take the nose of the Mk 16 from immediately in front of the cockpit forward, including the air intake.
Unless I have missed something, that would be a completely accurate Mk 8 built from reused 3D parts of existing AH Spitfires. The models may not be able to be broken down and parts recombined that way, but if they can....
Not meaning to sound pushy or like I am trying to tell you how to do your jobs. I just really want the Mk VIII and if I even have a small chance of suggesting something useful I'll take it.

Dan, Kev, have I missed anything about the Mk VIII in that parts list?