That explains that then!
Geo, all the ICM Spitfire kits are the same basic kit, just different decals, so any would do (apart from low-back MkXVI of course), so yes, that's the right kit.
Evan, there wasn't a Spitfire MkIXb as such. Because it was the first cannon-armed Spit after the MkV, and cannon armed MkII and MkV were know as 'B's, it was called the MkIXb by pilots and ground crew, and even sometimes recorded as such on official documents. It was in fact originally fitted with the 'C' wing - two cannon and four browning MGs.
I actually fell foul of this description about 25 years ago, when I converted a Hasegawa 1/32nd scale MkV into a 485 (NZ) Sqn aircraft, going off info describing the aircraft as MkIXb, including mention in Johnnie Houlton's book, and presuming the first ones had the 'B' wing. I therefore left the MkV type bulges in place, and altered the cannon and, of course, the rest of the airframe!
You can use a kit with a normal 'C' wing, or alter a 'E' wing if stuck, but it was definitely not the wing and bulges as seen on the MkVb.