[TheGrunch]

Ah, so it's definitely not appearing in Quick Missions, or in the list in the Loadouts screen? Could you post the contents of your user.ini in CODE tags?

My section for the Spit IIa looks like this:

[Aircraft.SpitfireMkIIa]
  conv _Gun03 Gun.Browning303MkII 100 100
  conv _Gun06 Gun.Browning303MkII 100 100
  conv _Gun00 Gun.Browning303MkII 100 100
  conv _Gun01 Gun.Browning303MkII 100 100
  conv _Gun07 Gun.Browning303MkII 100 100
  conv _Gun02 Gun.Browning303MkII 100 100
  conv _Gun05 Gun.Browning303MkII 100 100
  conv _Gun04 Gun.Browning303MkII 100 100
  belt _Gun03 Gun.Browning303MkII MainBelt 9 11
  belt _Gun06 Gun.Browning303MkII MainBelt 9 11
  belt _Gun00 Gun.Browning303MkII MainBelt 9 11
  belt _Gun01 Gun.Browning303MkII MainBelt 9 11
  belt _Gun07 Gun.Browning303MkII MainBelt 9 11
  belt _Gun02 Gun.Browning303MkII MainBelt 9 11
  belt _Gun05 Gun.Browning303MkII MainBelt 9 11
  belt _Gun04 Gun.Browning303MkII MainBelt 9 11
  beltPreset "AP-I 100m" _Gun03 Gun.Browning303MkII MainBelt 9 11
  beltPreset "AP-I 100m" _Gun06 Gun.Browning303MkII MainBelt 9 11
  beltPreset "AP-I 100m" _Gun00 Gun.Browning303MkII MainBelt 9 11
  beltPreset "AP-I 100m" _Gun01 Gun.Browning303MkII MainBelt 9 11
  beltPreset "AP-I 100m" _Gun07 Gun.Browning303MkII MainBelt 9 11
  beltPreset "AP-I 100m" _Gun02 Gun.Browning303MkII MainBelt 9 11
  beltPreset "AP-I 100m" _Gun05 Gun.Browning303MkII MainBelt 9 11
  beltPreset "AP-I 100m" _Gun04 Gun.Browning303MkII MainBelt 9 11
  weapons 1
  loadout "AP-I 100m" SpitfireMkI_WingGuns Default

EDIT: BTW, user.ini is in My Documents/1C SoftClub/il-2 sturmovik cliffs of dover