The MkXVI was the last variant to use the Merlin and was basically a MkIX airframe fitted with the license built Packard Merlin rather than the Rolls unit. The first production Spitfire to use the Griffon was the limited production MkXII. (which was also the only Griffon Spit to run a four blader, not counting the XV and XVII Seafires) Then came the Griffon powered MkXIV, followed by the Merlin powered XVI, and all subsequent marks from the XVIII through the 24 used the Griffon. Keep in mind the mark numbers were assigned during development and they did not always get introduced into service in that order. For example, when they decided to upgrade the MkV Spit it was supposed to be followed by the MkVIII. However, because the number of engineering changes needed for the MkVIII were delaying its introduction, the MkIX was quicklly worked up as a stop gap fill in. Therefore, the MkIX actually preceeded the MkVIII into service. Hope that makes sense!