I wanted to use a gasser, so I converted this plane to a P-36 with a radial cowling. There is a thread about this on here somewhere. I used standard Futuba 3004 servos for every thing. So far I have 80 flights or so on this airplane with no problems. With the P-40 cowling I think any good four stroke 91 to 120 will work. The airframe is fairly light so I don't think you need a 120. With the 90 degree exhaust manifold and a flexible exhaust you can keep the muffler etc inside the cowling. The kits landing gear is screwed up. If you want to make it more scale, 4" wheels are scale size. You will need to move and inlarge the wheel wells. I used Century Jet retracts for the Top Flight P-40, special ordered with the strut made 1/2 inch longer than standard. This puts the center of the wheel half way between the wing tube and the flap so you can use the large wheels. You will have to redo the retract mounting blocks.