Am I being obtuse or wouldn't the centre of gravity have to be in approximately the same position as any other Spitfire, i.e. pretty well cock on the lift centre of the wings?
I thought the Mark XIV was based on the fuselage of the Mark VIII which was already structurally superior to the earlier Marks? I know that old Willy was quite clever with the design of the Bf109, specifically with the machined bulkheads which carried the stresses of the engine, wings and landing gear, but clearly Joseph Smith was similarly competent so I think it's a safe assumption that the Mark XIV could handle the structural loads associated with the additional power and weight.
What interests and has always confused me was the stability issue, especially using the Bf109 as a comparison:
I thought a larger polar moment of inertia translates to greater inertial stability, not less. I'm not knowledgeable enough about the minutiae of aircraft design to foresee a fundamental difference, but in other vehicles a larger, or in this case a longer, distribution of the mass about its centre of gravity tends to make a vehicle
more docile and less inclined to change its direction quickly. Thus I would have assumed the the Mark XIV would bounce around less not more. Must be missing a vital piece of understanding

How can essentially the same change: i.e. adding a heavier and more powerful engine to an airframe designed for a lighter less powerful one, in the case of the Bf109 make its handling more docile, more controllable in a vertical stall and a more docile gun platform do the inverse in the Spitfire equivalent?