For the longest time I had wondered how Supermarine evolved the Spitfire into the Spiteful, I was fairly certain that at the very least all the bottom of the fuselage from the datum longeron (that's the horizontal panel line you see on most Spitfire models that is about mid height of the fuselage) downwards was really all Spitfire. The tail assembly would be interchangable between the two aircraft and the engine and mounting frames are the same too. But I couldn't figure out what they did to the top half of the fuselage. Then it came to me ----
Because the Spiteful is a bubble top, I kept looking at the bubble top Spitfires (especially the later ones) as to what did they did to convert the rest of the fuselage but I suddenly realized that I was looking at the wrong Spitfire type, I should have been looking at a 'standard' Spit, not the bubble top.
Why you might ask, well for one thing the rear fuselage profile matches a Spiteful's almost exactly, and as has been pointed out to me, three Mk.VIII's were originally assigned to the Spiteful project which should give a clue as to the basics of the Spiteful. I recently got hold of the highly touted Morgan and Shacklady book called 'Spitfire-The History' and I've now read what others had pointed out and actually confirms just about all I've figured out.
So this project was mainly to confirm to myself that a standard Spitfire could be converted into a Spiteful. I was amazed at just how easy it was too. Below is a pic of a standard Spitfire, a Mk.21 to be exact, and what you see in white and the lighter grey over the engine, is all I changed to get a Spiteful fuselage (with Spitfire wings though and the Mk.22 tail assembly)