Firewall back, the mk II and IX were very similar. The nose on the IX was longer to accomodate the two stage merlin 60 series. The wing shapes were identical, the major difference being in the armament fitted. One major difference is the oil cooler in the mk II was round vs the symetric coolers on the mk IX.

Your particular Spit was converted to a mk V in 1942. I will see if I can dig out some more info out of my books tonight....