Wish granted, the P-39 with a 20mm hispano is a P-400, just take an olive drab skin and you are good to go.
/actually liked flying the P-39 with a 20mm, one scenario I shot down 9 Zeroes with it, the ammo is pretty nice, I gambled from the 37mm - I simply couldn't hit crap with it and figured the 20mm would help me better on snap shots and it worked out.
//it was a scenario about Lae, the Zeros had to scramble and the P-39s strafe down the airfield, however most of us were gunning to see how many zeroes we could kill, it was a pretty nice air battle.