Hi Joe,

The biggest difference about the MK IIa and the MK IX is the lenght of the Spit 29ft 11 ins for the MK IIa and 31 ft 4ins for the MK IX wingspan is for both the same 36ft 10ins.
Most of the MKII Spits had a Merlin XII engine with 3 blades there was one with a Merlin 47 and he or she had 4 blades.
The MKIX had a lot of different engine but all Merlins with 4 blades.

Most of the MKIX's had a rounded tail and also a fixed tail wheel.
The MKVIII had a pointed tail and the tail wheel wasn't fixed he could put it into his fuse.

The MKII has 8 Browning 0.303 machine guns and another antenna than the MKIX but that are little details off cours.

MKII had a 3 exhausts pipes and the MKIX 6 and as you mentioned a differend spinner.

Sorry for my bad english, hope you can do something with it.

Greetings
Tom