thanks guppy . So how come there is a 500lb weight difference in my reference book between the all up weight of the spit IX LFe and the XVI LFe?
Karnak's question is a good one. Which reference are you using? Spit the History has 9500 for both as the overload weight, as does Bruce Robertson's "Spitfire-The Story of a Famous Fighter" and Phillip Moye's "Profile-Supermarine Spitfire Mk IX" which also includes data on the XVI as they were the same airframe.
All three have different normal take off loads for the IX and XVI varrying from 7500 to 8200 for both. Again the key is all three are clear that the XVI designation was purely to differentiate between the English and American built Merlins that went into the Spit IX airframe.