While I am not an expert on the P-39, I have to agree with what others have already said. The major differences involve adornment, power plant and avionics.
One thing I can tell you though, is that the well known P-39,"Airacutie" was an early model, either a D, or an F. Could have even a P-400. There is some debate as to which mark she actually was. However, I can tell you with that she most definitely not an N.
I hope I didn't burst your bubble with that. Snooks however was either an N or Q, and both are almost identical so you should be good with that one.
That is a nice little you have there, and I also look forward to seeing her finished. Good luck, and get busy building!
Freddie from LI