Seafire is a Spit V, yes.
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I added the F6F to the RN as well. They had it from Dec 43. Alternatively, it can also replace the Seafire.
As for the Spitfire IX, well, no, we have plenty of setups where its left out, and some players like it too. The CT isnt just for everybody else. Whats wrong with the MC205, is it broken?