you see I had a long , very polite discussion with Karnak about the spit LFIX e and the spit XVI and the differences between them (or lack of) . He helped to point out why there "seemed" to be discrepancies in a a book i was reading as regards weights and fuel load outs ect (mostly down to the heavier weight of ammo ) . The Mk IX high altitude we have in game is a 1942/43 spit IX , IF we were to use spit IX from 1944 onwards then it would have the same load out as the in game XVI with full span wings and same fuel arrangement. The ONLY difference was the merlin 266 in the XVI uses a different supercharger that is chain driven not driven by exhaust like the Rolls Royce merlin 66. Yet this makes no difference to the amount compression of the fuel mixture .
What we are missing is the cut down fuselage spit IX (XVI) with bubble canopy . which came both in full span and clipped wing.