Nice looking P-40 Jim. I like the way you ended the canopy just behind the windows. I have built a couple, one with a Fox .40 BB. The engine was mounted upright and had just enough scale power but could have used more. Nice thing about it was you couldn't see the muffler as easy as it was the tilt down version. The second version was powered with an OS Max .40. Again, not over powered. I would go with the lightest .42 to .46 I could find and you will be happy with it. Built light, the P-40 will have a nice long glide when landing, Make sure you reinforce the landing gear blocks with 1/16" ply wood ribs or they will bust loose on a hard landing, don't ask me how I know! Good luck and have fun. Richard.