The trouble is that @ThrillerFan also recommends a very good line against the KG and one cannot play both lines at once. My own advice to people looking for a good line against the KG as Black is the same as my general opening advice to everyone. Have a look at what positions the lines lead to. In which of them are the good moves natural for you? When you find the line leading to that sort of position, Play That!
Beat the King's Gambit as Black!
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@Compadre_J highlights a very good defence indeed for Black. KG players hate it (although we often don't admit that in public). Back in the 1970s, KG players were desperate enough as to start analysing 3..., d6; 4. h4?! Which doesn't really work but mixes things up and is good for a giggle in Bullet because it's usually good for ten seconds on the clock. Will Black spot ..., Nf6 - h5 - g3 and/or work out the tactics involving ..., Be7 xh4+? Who knows?
I don't approve of that sort of stuff myself - I see chess through a lens akin to that of Botvinnik (the art of making logic beautiful), but we're all different.