use a kit of a Spitfire Mk IX to build a MkVIII.

Thought it would be nice to turn Tamiyas upcoming 1/32 Spitfire into an RAAF aircraft, but unfortually the RAAF didn't use the Mk.IX.

If you look at the sprue pictures, on Hannant's website, you'll see that there's a large cut-out, on the fuselage aft of the transport joint, so I'd say that Tamiya have plans for a Mk.VIII (even a VII,) since that's where the retractable tailwheel, for those Marks, would go. If you can't wait, the ailerons need shortening, and, although some will make much of the wing l/e fuel tanks, by 1943 panel lines and rivet "divots" were being filled and smoothed, so you'll only need to scribe in the filler points. Other than that, everything should be already in the kit (there are both types of rudder, for instance, and the tailplanes/elevators.) Apparently Tamiya are also supplying two upper cowlings, so you'll be OK, there, since the VIII never had the "hump" that was visible on the late IXs & XVIs.
Edgar