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Richard, a few details on the later mark Griffon Spitfires for you.Mk 14 (as hoped for in Burma) Griffon65, 37 litre liquid cooled V12, 2,035 horse power. 439mph at 24,500ft.
F24, Griffon 61,64 or 85, as before but 2,340hp, 454 mph at 26,000ft.
Just for interest sake the MkXIX(19) was the last so called, from the Mk19 onwards Spitfires became the Mk F20 before becoming the Valient, the Spitful and the Seafang, hope this helps.