You've got the cell count right, but you're a little off on the voltages:
3-cell = 11.1V
2-cell = 7.4V
Building from readily available packs, that's 3-cell + 2-cell + 2-cell, all connected in series. Do it twice, connect them both in parallel, and you're right on the money!
This sounds like one K - E - double-W - L kewl project! Of all the warbirds, the P-40 is probably my second favorite after the Corsair. My first successful flying experience was with a little Cox control line P-40. I'm still dizzy and puking from it almost 20 years later
