ΔE 18.9, loose: different enough that you should pick on purpose. Green Ochre is noticeably darker, more muted than Flak Gun Yellow.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Green Ochre is noticeably darker, more muted than Flak Gun Yellow.
The same difference applies the other way round: Flak Gun Yellow is noticeably lighter, more saturated.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Flak Gun Yellow on the colour wheel See Green Ochre on the colour wheel
All matches: Flak Gun Yellow equivalents · Green Ochre equivalents