A Spit XVI is only a Spit IX with a Packard built Merlin. The AH Spit IX is a 1942 aircraft with C type wing and standard wingtips. The AH Spit XVI is a late 44 version with the E wing, clipped wingtips and extended fin and rudder. The convention in skinning terms is to skin any Spit IX that has an E wing (cannons outboard of the 0.5in guns) on the Mk XVI skin as this is closer in shape and performance to the real aircraft.
I'm a bit dubious about the accuracy of the Osprey book now. The aircraft Twinboom posted is described as a Mk IXE but the cannon layout shown on the profile is a Mk IXC. I suspect its more likely to be an E and that the artist screwed up. Without a photo its hard to tell.
The profile of my original Spit IX skin is actually shown twice inside the Osprey book with different descriptions, one says 1944 the other 1948. I think I'll shelve this skin until I get better info on it.